The heat transfer coefficient of an uninsulated greenhouse of 4.59 W/m/sup 2/K can be reduced to a value of 1.93 to 3.59 W/m/sup 2/K, depending upon the type of material used and the effectiveness of closure of the mechanical system. The open, woven-cloth materials tested offer significant energy savings, handle well mechanically, drain condensate, and have a potential to double as shading materials in the summer. The thermally opaque and air tight materials tested offer significantly increased energy savings, but provision must be provided to drain off condensation if the materials do not self drain. Some of these materials were found somewhat harder to handle and bulkier to store than the open, woven cloth. It has also been shown that aluminizing the upper surface of a curtain can increase heat savings if the edges are well sealed. Also, some opaque and aluminized materials have a potential use for photoperiod control.