Physical Properties Of Foams Research Articles

Transmission of vertical vibration through a seat cushion at the seat pan: Effect of foam physical properties during different excitation magnitudes

The vibration characteristics of car seats directly influence the ride comfort. Polyurethane foam is the key part of a seat, and its physical parameters have an important impact on the seat. In this study, the influence of the foam thickness and foam hardness on the vibration characteristics of seat cushion with different excitation magnitudes was investigated by using transmissibility and seat effective amplitude transmissibility (SEAT) value. First, vibration tests were carried out at a vertical vibration simulator with width-limited white noise vibration frequencies from 0.5 to 20 Hz with root-mean-square (r.m.s.) values of 0.4, 0.8, and 1.2 m/s2, the acceleration at the platform and the body-foam interfaces were measured to calculate the transmissibility, and the influence of the foam physical properties on the transmissibility was analyzed. Then, the SEAT value was introduced to assess the vibration isolation efficiency of the foam cushion, and the influence of the foam physical properties of the foam cushion on the vibration isolation efficiency was analyzed. With increasing thickness of the foam and decreasing hardness of the foam at the seat pan, the peak transmissibility increased and the resonance frequency decreased. The SEAT values show that increasing the foam thickness is beneficial to the improvement of the vibration isolation efficiency of the seat, but there is a diminishing return; the combination of physical parameters of low hardness and high thickness could make the vibration isolation performance of the seat better. In addition, the nonlinearity of human-seat system during different vibration magnitude was found.

Tropical Red Fruit Blends: The Effect of Combination of Additives on Foaming, Drying and Thermodynamic Properties

Blends combine advantageous characteristics of each species, resulting in products with different flavors and nutritional substances. Moreover, transforming them into powder provides numerous advantages. This work evaluated the properties of three blended foam formulations made from the pulps of tropical red fruits (acerola, guava and pitanga) to determine the foam layer drying kinetics and thermodynamic properties. The foam formulations were prepared by mixing the three pulps in equal proportions (1:1:1), all added with 6% albumin and 1% stabilizing agent. The foams were analyzed for density, volumetric expansion, stability and porosity in six mixing times. Subsequently, they were subjected to drying in an oven with forced air circulation at 4 temperatures, with a layer 0.5 cm thick. Seven mathematical models were fitted to the drying kinetics experimental data to determine the effective diffusivity and thermodynamic properties of the samples. The best mixing times were 5 min for the E2 sample and 30 min for the others. Formulation E2 presented the best results in the foam physical properties, and E3 presented the shortest drying times. All models tested were satisfactorily adjusted, but Page’s model was the most adequate to describe the process. Sample E3 showed the highest diffusivity and sample E2 the lowest activation energy. The drying temperature increase caused reductions in enthalpy and entropy, as well as an increase in Gibbs free energy, indicating an endergonic process. The combination of additives incorporated into the blend influences the drying process: formulation E2 shows greater efficiency in removing water, and formulation E1 presents the highest energy demand.

Rational Design of a Polyurethane Foam.

Polyurethane (PU) foams are exceptionally versatile due to the nature of PU bond formation and the large variety of polymeric backbones and formulation components such as catalysts and surfactants. This versatility introduces a challenge, namely a near unlimited number of variables for formulating foams. In addition to this, PU foam development requires expert knowledge, not only in polyurethane chemistry but also in the art of evaluating the resulting foams. In this work, we demonstrate that a rational experimental design framework in conjunction with a design of experiments (DoE) approach reduces both the number of experiments required to understand the formulation space and reduces the need for tacit knowledge from a PU expert. We focus on an in-depth example where a catalyst and two surfactants of a known formulation are set as factors and foam physical properties are set as responses. An iterative DoE approach is used to generate a set of foams with substantially different cell morphology and hydrodynamic behaviour. We demonstrate that with 23 screening formulations and 16 final formulations, foam physical properties can be modelled from catalyst and surfactant loadings. This approach also allows for the exploration of relationships between the cell morphology of PU foam and its hydrodynamic behaviour.

Synthesis of novel carbon-supported iron oxide sorbents for adsorption of dye from aqueous solutions: equilibrium and flow-through studies

Textile effluents contain dyes that negatively affect water bodies and inhibit photosynthesis by reducing sunlight penetration. This study investigated the adsorption capacity of an iron oxide sorbent immobilised on naturally derived carbon foam for the removal of organic methylene blue dye from water. In this study, the carbon precursor and iron oxide precursor were mixed and carbonised in a single vessel. Baking and carbonization of the natural grain combination produce a porous structure that can act as an effective support for the iron oxide particles. The carbon foam prepared had a self-assembled structure with flour as a basic element. Sorbents of 6 weight (wt)%, 15 wt% iron, and a 0 wt% iron control sample were prepared. Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) techniques were used to examine the synthesised carbon foam physical properties and surface morphology. The adsorption capabilities were investigated in batch tests by determining the effects of an increase in iron content, sorbent dosage, contact time, and dye concentration. Breakthrough curves were obtained by varying the height of the sorbent bed and varying the flowrate of the dye solution. A higher bed height corresponds to a greater amount of adsorbent. The breakthrough and equilibrium adsorption capacities were found to increase with increasing bed height. When the flow rate is high, the dye solution leaves the column before equilibrium, resulting in shorter breakthrough and saturation times. Higher bed heights and lower flow rates resulted in optimal dye removal in the flow through the system. Breakthrough time increases with increasing iron content. The 15 wt% iron sample displayed superior adsorption capabilities than the 6 wt% sample, while the 0 wt% iron control sample displayed minimal adsorptive capabilities. The pseudo-first order kinetic model was the best fit model for this study (R2 > 0.96), and the adsorption equilibrium is best described by the Freundlich isotherm (R2 > 0.99). The results showed that an iron oxide sorbent immobilised on carbon foam made from natural sources is a good adsorbent for removing methylene dye.

A novel method to develop nanocomposite bimodal foams containing expandable polymeric microballoons: microstructural characteristics

This study aims to develop a novel technique in manufacturing nanocomposite bimodal foams containing expandable polymeric microballoons. Low density polyethylene syntactic foams were prepared via injection molding process, afterwards, a batch refoaming method was utilized to create bimodal structure. The effects of microballoon and nanoclay content and foaming time and temperature on microstructure and physical properties of foams were investigated. The results revealed that refoaming leads to a considerable decrease in density due to nucleation of microcells along with re-expansion of microballoons, as well as CO2 diffusion in voids between the matrix and microballoon surfaces. Microballoon content has no significant effect on cell size of bimodal foams, while a great growth in cell density was observed as its content increased. Results also indicated that at low and high foaming temperature and time, melt strength and gas loss are the overcoming phenomena, respectively leading to an optimal processing temperature and time.

Foaming characteristics and impact of ethanol pretreatment in drying behavior and physical characteristics for avocado pulp powder obtained by foam mat drying.

The objective of this study was to optimize the production of powdered avocado using foam mat drying. In order to achieve this, the effect of Emustab® (4, 6, and 8% w/w), goat's milk (10, 15, and 20% w/w), and whipping time (15, 20, and 25min) on the foam physical properties of avocado pulp were evaluated. In addition, the influence of ethanol pretreatment on the drying kinetics, thermodynamic properties, and physicochemical characteristics of the powders was also assessed. An experimental design 23 with three central points was used in this study and optimized foam conditions were dried at 50, 60, and 70°C, with a fixed air speed of 1.5m/s. Empirical and diffusive models (boundary conditions of the third type) were adjusted to the experimental data to describe the drying kinetics and to determine the process activation energy and thermodynamic properties. The final products were characterized regarding their physical properties. Optimized foam mat drying conditions were achieved when avocado pulp was whipped for 15 min and 8% of Emustab® and 20% of powdered goat milk were used as foaming agents. The use of an ethanol pretreatment and higher drying temperature (70°C) resulted in higher drying rate (1.6×102 /min) and shorter processing time (270min). The ethanol pretreatment reduced the activation energy and Biot number and led to more uniform moisture distribution. The physical properties, such as water content, water activity, bulk, and tapped densities decreased with an increase in drying temperature and pretreatment with ethanol, whereas water absorption capacity increased. PRACTICAL APPLICATION: In this work, new information about the drying kinetics and mass transfer of the foam mat avocado pulp using ethanol as pretreatment is obtained. The results will contribute to the optimization production avocado foaming and powder. Ethanol pretreatment can represent an alternative to minimize the negative impacts on drying process and can be surely suggested as an industrial application.

Sensitivity Analysis of the Parameters Affecting Bottom-hole Pressure during Foam Underbalanced Drilling

With many advantages of protecting reservoir, increasing drilling speed and high capacity in carrying cuttings, foam drilling is suitable for drilling through the aquifer and natural fractured formation, and has been developed fast since 1990s. However, the change of the foam physical properties along wellbore, and the flowing state of the foam in the annulus is complex. Therefore, it is difficult to optimize the design of hydraulic parameters for foam drilling. In order to solve this problem, the mathematical model for foam-cutting flowing in annulus has been developed. In addition, the sensitivity analysis has been conducted about the factors affecting the parameters of foam drilling and the characteristics of foam flowing. The analyzing results can provide the foundation for designing the hydraulic parameters of foam drilling.

Material Characterization of Hierarchical Tunable Pore Size Polymer Foams Used in the MARBLE Mix Morphology Experiment

One of the great challenges of inertial confinement fusion and high energy density experiments is understanding the effects of mix on thermonuclear burn. The MARBLE campaign, conceived at Los Alamos National Laboratory, aims to gather new insights into this issue by utilizing unique target capsules containing polymer foams of variable pore sizes, tunable over an order of magnitude. Such capsules allow the degree of initial heterogeneity to be controlled experimentally for the first time. Here, we describe the various characterization efforts used to gain understanding of the chemical structure and behavior of the foam. Previous experiments were not sensitive to foam physical properties, and the MARBLE platform has aided in the development of techniques to measure foam properties such as deuterium content, density variation, hydrogen adsorption, and pore size and volume distribution.

Effectiveness of microwave processing approach and green blowing agents usage in foaming natural rubber

This study mainly concerns the role of foam heating process techniques and its impact on cellular micromorphology, density and gas liberation mechanism of natural rubber foam with distilled water as blowing agent. Three different modes of heating process techniques and varying amount of distilled water have been examined on the foam density and cellular morphology, having rather identical morphological formation, cell distribution and relatively reducing densities but significant cell wall thickness. It is deduced that the increase in the water loading substantially affects the decrease in the foam densities, cell uniformity and stability. However, the heating process techniques influence the cell distribution and stability more than the amount of water content loading. The combine microwave oven process technique has improved the process of moisture diffusion into the water-blown open cell natural rubber foam unlike the slower procedure of conventional heating technique. In addition, the natural rubber foam physical properties and microstructure is improved better than the conventional heating technique. In all the simultaneous combine microwave oven technique is the best among the evaluated technique from the experiment because of density increment, cell distribution, pores flaccidity and uniform cells.

Solution Construction to a Class of Riemann Problems of Multiphase Flow in Porous Media

Fluid displacement in porous media can usually be formulated as a Riemann problem. Finding the solution to such a problem helps shed light on the dynamics of flow and consequently optimize operational parameters such as injected fluid composition. We developed an algorithm to find solutions to a class of Riemann problems of multiphase flow in porous media. In general, the solution to a Riemann problem in state space is a curve connecting the left and right states of the problem. The solution curves studied here are composed of classical wave curves. For a given Riemann problem, our procedure to find the solution consists of three steps: (1) guess the initial lengths of the solution’s constitutive wave curves; (2) construct each wave curve off the last state of its antecedent wave curve; and (3) iterate over the lengths of the constitutive wave curves, using an iterative solver, until the solution curve ends at the right state of the problem. We used benchmark cases from literature to verify the accuracy of the developed algorithm. Using the developed algorithm, we found solutions to some challenging cases where otherwise numerical simulators would be needed to find the type of the involved waves (i.e., rarefaction, shock or composite waves) and the coordinates of the middle states in the state space. Saturation profiles, oil cut and oil recovery for all the studied cases were computed. This information will assist us to: gain insight about the dynamics of flow, interpret core flooding measurements, assess the accuracy of developed models for foam physical properties, and verify the results of numerical simulators.

Numerical simulation of foam flow pressure drop in coiled tubing spiral section

A user-defined function and a numerical simulation method were used to analyze the pressure drop of foam flow in the coiled tubing spiral section, and the calculated pressure drop was compared with the simulated pressure drop. For foam flow in the straight section, as the influences of acceleration pressure drop and actual velocity profile were considered, the simulated pressure drop is higher than the calculated pressure drop. For foam flow in the spiral section, due to the compressibility, the foam physical properties change with pressure. Therefore, at different outlet pressures, the velocity profile and density profile are different at the same spot. Centrifugal force makes the velocity profile unsymmetrical. Outlet pressure, gas injection rate, and curvature have significant influence on pressure drop. During the hydraulics design for coiled tubing drilling with foam, the foam injection pressure should be as high as possible to decrease the pressure drop of foam flow in the spiral section.

Design of Polyol for Rigid Polyurethane Foam （spray）

Rigid polyurethane foams are used in various fields such as building applications, freezing and refrigerationequipment applications, civil engineering applications, marine vessel applications and the like, due to theirself-adhesive properties and high insulation performance. Energy saving for reducing carbon dioxide emissionsis now an important issue even in the industrial world. And rigid polyurethane foams with high thermalinsulation performance are increasingly required to reduce energy consumption. Since the rigid polyurethanefoam for spraying has self-adhesiveness and can form seamless high insulation layer, it is often used in anapartment or a public building. Though hydrofluorocarbons （HFCs） have high global warming potential, theyhave been used as blowing agents until the present time. But, in recent years, the substitution of HFCs forhydrofluoroolefins （HFOs） which have low thermal conductivity of gas and low global warming potential isprogressing as alternative blowing agent. However, polyol system using HFOs has some problems with storagestability and physical properties of foams. We focused on the solubility of HFOs to polyols, and have developednew polyols with high reaction activity, whose polyol system shows excellent storage stability and improvedphysical properties of foams. In addition, due to aromatic structure of Mannich condensate of these polyols,improvement in flame retardancy of foams can be also expected.Key words : Rigid polyurethane foam, Self-adhesiveness, HFCs, HFOs

Thermal Expansion Properties of Fused Borosilicate Syntactic Foams

The thermal properties such the coefficient thermal expansion, α (CTE) of fused borosilicate syntactic foam was determined using dimensional changes of a temperature gradient plot. The CTE was measured and found to be achieved the value lower than the vinyl ester resin matrix when mixing with different weight percentages of the glass microballoon ranging from 2 wt.% to 10 wt.% using a thermomechanical analyzer (TMA). These results showed that it has a strong relationship with the syntactic foam physical properties such density, radius ration,cavity porosity and matrix porosity. Experimental results showed that the CTE decreases when glass microballoons are added into the composites measured at different temperatures ranging from 30 °C to 70 °C. The CTE from the experimental results were also analysed using Turner’s modification model for composites for its suitability for thermal expansion of syntactic foams.

Preparation and structural characterisation of model cellular vitreous carbon foams

The aim the present work was to produce carbon foams with as different as possible porous structures but with similar composition and carbon texture for studying precisely the influence of different structural parameters such as density, cell size or interconnectivity on the physical properties of these foams. Over 60 different cellular carbon foams were obtained by pyrolysis of phenolic-furanic rigid foams, whose structure was tailored through some changes in the formulations. The structures of all of these materials were thoroughly characterised through scanning electron microscopy (SEM) and X-Ray microtomography. Both methods proved to give very consistent results, justifying the use of the simpler one, i.e., SEM. Very broad ranges of bulk densities (0.015≤d≤0.333gcm−3) and of average cell diameters (100≤D≤5000μm) were obtained. Despite these very different morphologies, elemental analysis, helium pycnometry and Raman spectroscopy studies showed that the carbon constituting the foams can be considered as identical. The results presented here should be used as a basis for the most thorough and extensive studies of physical properties of vitreous carbon foams.

Physical characterization of freeze-dried foam prepared from aloe vera gel and guar gum

Background: Foams are colloidal dispersions of a gas suspended in a dispersing phase, which consisting of a semi-freeze-dried or viscous liquid phase. The physical properties of food foams are the result of the bubble characteristics and their spatial arrangement. Objectives: The aim of this work was to obtain foams of A. vera gel and guar gum and describe the changes in their physical properties and microstructure during freeze-drying using the fractal dimension concept and image analysis techniques. Methods: The porosity, density, and volume expansion factor of the fresh foams that were based on the A. vera foams were determined. The kinetics of foam texture, color, porosity and microstructure of the freeze-dried foams were obtained. The fractal texture dimension of surface (FDSDBC) and microstructure (FDESEM) of the foams were determined as indicators of structural changes after freeze-drying. The guar gum concentrations used to obtain the A. vera prefoam were expressed in w/w as F1 (control simple without gum), F2 (2%), F3 (4%) and F4 (6%). Results: We obtained stable freeze-dried foams of Aloe vera gel and guar gum. The porosity, density and volume expansion factor of the fresh and freeze-dried foams were affected by the addition of the guar gum. Changes in the topology of the freeze-dried foam surface during the drying process resulted in a high rugosity compared with the original smooth surface. The microstructure of the dried foam samples suggested a relationship between the gum concentration of the prefoam A. vera gel mixture and the physical properties before and after freeze-drying, such as an increase in the microstructural alterations and surface roughness during freeze-drying. The roughness of the freeze-dried foam surface, described by the FDSDBC represented the macroscopic physical changes of the samples and correlated with the changes in the foam microstructure, which were described by the fractal dimension of the Environmental Scanning Electron Microscopy ESEM microphotographs (FDESEM). Conclusions: The digital analysis of the structure and porosity of the freeze-dried foam can be used to quantify the effect of gum concentrations on the morphological features and physical properties of foams during freeze-drying.

Comment to: Volume displacements from an incompetent great saphenous vein during a standardised Valsalva manoeuvre, by Lattimer CR, Kalodiki E, Azzam M, Geroulakos G. Acta Phlebologica 2012;13:25-30.

Reflux duration longer than 0.5 s is the cut-off point for the diagnosis of valvular incompetence. It is induced by a calf compression/release maneuvre (CCRM) in a weight-loaded position, with a full venous reservoir. CCRM is a pre-valve challenge test; reflux stops when the reservoir is full. In contrast, a Valsalva maneuvre (VM) is a post-valve challenge test and also a validated technique to induce reflux. It is performed in a supine position, when the venous reservoir is only partially filled. The Authors measured the volume of blood displaced during a standardized VM within an incompetent GSV (18 patients C2, reflux until the popliteal crease). A standard VM was performed by taking a deep breath during 3 s, a strain during the next 3 s, and then a relaxation during the final 3 s. GSV diameters during stain and relaxation were measured just distal to the SFJ. Volume flow in cc/min (time average mean velocity x diameter) multiplied by 3/60 gave volume displacement in 3 s. A median of 25 mL blood was displaced into the GSV over 3 s during straining with only 9 mL blood out of the GSV during the following 3 s of relaxation. As far as the volume is concerned, the different physical properties of foam must be referred to and the displaced foam volumes are likely to be lower. During ultrasound guided foam sclerotherapy (UGFS), VM is unavoidable (leg movements, cough, head lifting, strains, stocking application) and bolus displacement of foam into deep veins, and blood/foam mixing may cause concern over safety and efficacy. Protocols should be formulated to minimize the VM risks (stocking application, avoid standing, talking and coughing soon after the injection). Putting on a below-the-knee stocking before the procedure may be of benefit. This study has also shown that reflux duration following a VM can be determined by the physician and not by the pathology of the disease.

Reinforcement of soy polyol‐based rigid polyurethane foams by cellulose microfibers and nanoclays

AbstractWater‐blown rigid polyurethane foams from soy‐based polyol were prepared and their structure–property correlations investigated. Cellulose microfibers and nanoclays were added to the formulations to investigate their effect on morphology, mechanical, and thermal properties of polyurethane foams. Physical properties of foams, including density and compressive strength, were determined. The cellular morphologies of foams were analyzed by SEM and X‐ray micro‐CT and revealed that incorporation of microfibers and nanoclays into foam altered the cellular structure of the foams. Average cell size decreased, cell size distribution narrowed and number fractions of small cells increased with the incorporation of microfibers and nanoclays into the foam, thereby altering the foam mechanical properties. The morphology and properties of nanoclay reinforced polyurethane foams were also found to be dependent on the functional groups of the organic modifiers. Results showed that the compressive strengths of rigid foams were increased by addition of cellulose microfibers or nanoclays into the foams. Thermogravimetric analysis (TGA) was used to characterize the thermal decomposition properties of the foams. The thermal decomposition behavior of all soy‐based polyurethane foams was a three‐step process and while the addition of cellulose microfibers delayed the onset of degradation, incorporation of nanoclays seemed to have no significant influence on the thermal degradation properties of the foams as compared to the foams without reinforcements. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Wellbore Flow and Heat Transfer of Drilling with Foam

On the basis of special physical properties of foam drilling fluid, a mathematical model of foam flow and heat transfer in a wellbore was established, and the solution of the model was proposed. Employing the established mathematical model and its solution, numerical calculation was conducted to analyze the effect of wellbore heat transfer on the hydraulic parameters of foam drilling. The results indicated that foam temperature in a drilling pipe was always lower than that in the annulus and formation temperature. At the bottom of the annulus, foam temperature was lower than the formation temperature, whereas in the top of the annulus, foam temperature was higher than the formation temperature. Most important, with increasing well depth, liquid injection rate, and gas injection rate, the deviation between foam temperature at the bottom of the annulus and formation temperature increased. Wellbore heat transfer not only resulted in increased foam quality in the top of the annulus, bottom pressure, and minimum gas injection rate but also a decrease in the foam quality at the bottom of the annulus and minimum cutting transport velocity. Therefore, the stability and cutting transport capacity of foam decreased. In addition, foam density and Fanning friction coefficient were affected by wellbore heat transfer. Although to a certain extent wellbore heat transfer has an effect on hydraulic parameters of foam drilling, the effect was limited and could be counteracted by increasing gas injection rate and back pressure.

Effects of sucrose on egg white protein and whey protein isolate foams: Factors determining properties of wet and dry foams (cakes)

The effects of sucrose on the physical properties of foams (foam overrun and drainage ½ life), air/water interfaces (interfacial dilational elastic modulus and interfacial pressure) and angel food cakes (cake volume and cake structure) of egg white protein (EWP) and whey protein isolate (WPI) was investigated for solutions containing 10% (w/v) protein. Increasing sucrose concentration (0–63.6 g/100 mL) gradually increased solution viscosity and decreased foam overrun. Two negative linear relationships were established between foam overrun and solution viscosity on a log–log scale for EWP and WPI respectively; while the foam overrun of EWP decreased in a faster rate than WPI with increasing solution viscosity (altered by sucrose). Addition of sucrose enhanced the interfacial dilational elastic modulus ( E′) of EWP but reduced E′ of WPI, possibly due to different interfacial pressures. The foam drainage ½ life was proportionally correlated to the bulk phase viscosity and the interfacial elasticity regardless of protein type, suggesting that the foam destabilization changes can be slowed by a viscous continuous phase and elastic interfaces. Incorporation of sucrose altered the volume of angel food cakes prepared from WPI foams but showed no improvement on the coarse structure. In conclusion, sucrose can modify bulk phase viscosity and interfacial rheology and therefore improve the stability of wet foams. However, the poor stability of whey proteins in the conversion from a wet to a dry foam (angel food cake) cannot be changed with addition of sucrose.

Foams Prepared from Whey Protein Isolate and Egg White Protein: 1. Physical, Microstructural, and Interfacial Properties

Foams were prepared from whey protein isolate (WPI), egg white protein (EWP), and combinations of the 2 (WPI/EWP), with physical properties of foams (overrun, drainage 1/2 life, and yield stress), air/water interfaces (interfacial tension and interfacial dilatational elasticity), and foam microstructure (bubble size and dynamic change of bubble count per area) investigated. Foams made from EWP had higher yield stress and stability (drainage 1/2 life) than those made from WPI. Foams made from mixtures of EWP and WPI had intermediate values. Foam stability could be explained based on solution viscosity, interfacial characteristics, and initial bubble size. Likewise, foam yield stress was associated with interfacial dilatational elastic moduli, mean bubble diameter, and air phase fraction. Foams made from WPI or WPI/EWP combinations formed master curves for stability and yield stress when normalized according to the above-mentioned properties. However, EWP foams were excluded from the common trends observed for WPI and WPI/EWP combination foams. Changes in interfacial tension showed that even the lowest level of WPI substitution (25% WPI) was enough to cause the temporal pattern of interfacial tension to mimic the pattern of WPI instead of EWP, suggesting that whey proteins dominated the interface. The higher foam yield stress and drainage stability of EWP foams appears to be due to forming smaller, more stable bubbles, that are packed together into structures that are more resistant to deformation than those of WPI foams.