Asphalt insulation belts (hereinafter referred to as “AIP”) are traditional waterproofing material for roof constructions and lower structures. This article demonstrates the possibility of selecting water-proofing depending on bulk density. The density, unlike the thickness of surface density, can take into consideration the composition of the asphalt belt. The true composition affects the waterproof function of the asphalt belts and the bulk density can help when selecting correct water-proofing.