Most towable tubes are constructed of nylon with a denier rating that indicates the material’s strength (which can range from 420 for a single-rider towable to up to 840 deniers). Polyester is also quite common, typically reinforced with a PVC coating. PVC vinyl lines the bottoms of some tubes and is used for the bladders or inner tubes of most towable tubes. Tubes with coated bottoms glide smoothly over the water, causing less strain.