To insulate the castings tops, heat-insulating shells are made from peat-containing mixtures, which are characterized as inexpensive, non-scarce and environmentally friendly substances. However, due to their low strength characteristics and a high degree of fire hazard, their widespread use in foundry is limited. The article presents the results of research on the development of effective mixtures for insulating the steel castings tops using peat and borate compounds. The development of an effective heat-insulating mixture for heat insulation of castings on the basis of peat mass using glyceroborate of the general formula (СН2О)3ВОН, glyceroborate of oleic acid of the general formula С17Н33СООСН(СН2О)2ВОН and glyceroborate of stearic acid of the general formula С17Н35СООСН(СН2О)2ВОН. To achieve this goal, the following tasks were solved: determination of the tripoli content in the peat mass, at which the value of the thermal conductivity coefficient is 0.42 W/(m ∙ K) and the indicator of the mixture crumbling at this value; study of the influence of glyceroborates on binding properties of technical lignosulfonates; creation of a heat-insulating mixture from peat, tripoli, lignosulfonate and glyceroborates; study of crumbling, formability, ultimate compressive strength in a wet state and ultimate tensile strength in a dry state of an insulating mixture in dependence on the content of glyceroborates. Studies of the influence of glyceroborates on the binding properties of technical lignosulfonate have established an increase in its binding properties in relation to fillers by 35–39 %, which helps to reduce crumbling, improve formability and increase the strength properties of heatinsulating mixtures. Tests of mixtures consisting of peat, tripoli, lignosulfonate and glyceroborates for crumbling, formability, compressive strength of samples in a wet state and tensile strength of dry mixtures under tension showed that the addition of glyceroborate compounds improves the technological performance of the mixture. An effective heat-insulating mixture has been developed for the steel castings tops of the following composition, wt.%: peat mass — 60; tripoli — 20; technical lignosulfonate — 10–12; glyceroborate (oleic acid glyceroborate, stearic acid glyceroborate) — 8–10.