When faced with decision which thermal insulation to use we should know: thermal resistance of material, energy needed to produce it, and finnaly, its impact on the thermal comfort of the user. We can choode between natural thermal insulation materials, for example: cork, straw, wood fibres, sheep wool, coconut fibres, etc.; and synthetic thermal insulation materials, such as: polystyrene, polyurethane, perlite, mineral wool, blown glass, etc. We wanted to determine, if the size and type of chip particles have an effect on heat conductivity of the composites. We made 3 types of chipboards that had the same density (200 kg/m3), but different in size of the chips. One was made of chips smaller and equal to 1.5 mm; for the other 1.5 mm-6.14 mm were used; we mixed chips of all sizes for the third. We found that the type and size significantly affected heat transfer. The best insulation properties had the board made of 1.5 mm-6.14 mm sized chips, the worst that of straw board.