Heat losses in greenhouses may be substantially reduced by the use of heat reflecting blinds. Quantitative results are obtained solving a mathematical heat flow model by numerical methods. Special attention has been given to the emissivity and transmittance of the screen and the ventilation through screen and glass. The heat losses by condensation are obtained from a simultaneously solved moisture balance. In most cases condensation on the lower side of the screen influences the emissivity. An unexpectedly large part of the heat is transmitted by ventilation. The emissivity of the coated surface has been measured for a number of screen materials. The durability of the coatings is also taken into consideration. For greenhouse application it is always necessary to protect against corrosion.