Wetsuits are limited in their ability to preserve warmth by three factors: the wearer is still exposed to some water, the suit is compressed by the ambient pressure, reducing effectiveness at depth, and the insulating neoprene can only be made to a certain thickness before it becomes impractical to don and wear. The thickest commercially available wetsuits are usually 10 mm thick. Other common thicknesses are 7 mm, 5 mm, 3 mm, and 1 mm. A 1 mm suit provides very little warmth and is usually considered a dive skin, rather than a wetsuit. Wetsuits can be made using more than one thickness of neoprene, to put the most thickness where it will be most effective in keeping the diver warm. A similar effect can be achieved by layering wetsuits of different coverage. Some makes of neoprene are softer, lighter and more compressible than others for the same thickness, and are more suitable for wetsuits for non-diving purposes as they will compress and lose their insulating value more quickly under pressure, though they are more comfortable for surface sports because they are more flexible and allow more freedom of movement.