Because underwear is worn more every day, and the requirements for comfort are higher, underwear is generally designed with all-round fabrics, and underwear is not waterproof; Swimming trunks are usually worn when swimming in water, and are exposed to air and water for a long time, so the material of swimming trunks is required to be firm and elastic, not tight, opaque, waterproof and brightly colored. Because of daily wear and high requirements for comfort, underwear is generally designed with all-round fabrics, and underwear is not waterproof; Swimming trunks are usually worn when swimming in water and exposed to air and water for a long time, so the material of swimming trunks is required to be firm and elastic, not tight, opaque, waterproof and bright in color. Pants and swimming trunks are two different concepts. Swimming trunks are paired when swimming. As for underwear, if you swim in a pair of pure cotton underwear, you may fall off.