Manufacturers recommend using rigid venting material, not plastic vents that may collapse and cause blockages.
制造商推荐使用刚性材料的宣泄，而不是塑料喷口可能崩溃，并造成淤塞。
2
They are made of a rigidmaterial, like plastic, but some are made of leather or other soft materials.
矫正鞋垫通常由刚性材料，比如塑料、但也有些用皮革或其他柔软的材料做成的。
3
Another kind is thermoplastic polystyrene foamed plastic thermosetting and rigid polyurethane foams primarily organic heat preservation material, usually identified as combustible materials.