The suits are highly water resistant, and the water that does seep through gradually becomes warmed by the body, although if the suit is ill-fitting and large amounts of seawater penetrate, the water remains cold, making the diver feel as if he's wearing no suit at all.
潛水衣的質料是強力海綿狀的合成橡膠，下水後，會吸收少量水，合身的潛水衣，使進入的水受體溫影響變暖，不會與外面的冷水對流。若穿不合身的潛水衣，過多的空間使冷水能隨時進入，等於沒穿。