There are many types of oil felt paper, which can be divided into petroleum asphalt felt, coal asphalt felt, low-temperature resistant felt, powder faced felt, sand faced felt, colored sand faced felt, mineral wool paper felt, asphalt glass cloth felt, metal foil felt, hot-melt felt, self-adhesive felt, flame retardant felt, etc. according to the type of asphalt and spreading fabric, tire base material, functional characteristics, etc. Among them, petroleum asphalt felt can be divided into three specifications according to their grades: 200, 350, and 500. Each specification of felt has its specific application scenarios and performance characteristics.

The reason for the occurrence of hollowing in asphalt glass cloth and felt is often due to the high moisture content of the base layer of the membrane waterproof layer. Before the leveling layer is dried, the membrane waterproof layer is constructed to seal the moisture inside, and when exposed to hot gas, the waterproof layer swells up; When laying different types of oil felt rolls, if the pressure is not tight and the adhesion is not dense, the hot air generated during the operation will be trapped, causing the rolls to bubble and bulge. During construction, attention should be paid to the dryness of the base layer. During operation, it should be compacted and tightly adhered, and no gas should be trapped to prevent hollowing.