Skins are thin, and they are used for warm-water diving or used as a first layer under a wetsuit or drysuit. Traditional skins offer minimal thermal and abrasion protection. But they still provide some level of protection from stingers and cuts from sharp objects. Traditional skins are generally made from a spandex synthetic fiber (such as Lycra®).
Technical fleece is the new standard in tropical dive suits and undersuits for wetsuits and drysuits. A technical fleece has all the warmth qualities of a thin wetsuit but none of the buoyancy issues. It is often much more abrasion resistant and comes in many forms—from vest or short-sleeve tops to shorts or full-body suits.
Many divers use their standard wetsuits in the summer and add the technical fleece for more warmth in the winter. There are many brands on the market, but the high-end brands use a high-quality membrane. This membrane provides protection from wind chill and allows excess heat to vent through it, making the fleece very comfortable to wear on the trip home.
Skins are extremely easy to put on and come in all shapes, sizes, and colors. There are many styles available: Skins may have zippers on the front or back, stirrups to keep the legs part from riding up, and thumb loops to keep the sleeves in place.