When you first start diving there is one piece of equipment which is essential and you will use for almost every diving activity and that is an undersuit. The undersuit is designed to keep you warm while you are in the cold water. The temperatures of the water can reach extremely low levels which makes it absolutely essential that you keep your body temperature as high as possible when you are in the water.
Undersuits are used to provide extra warmth when diving and they are worn traditionally under a drysuit, however they are now great for wearing under wetsuits as well. Undersuits come in a wide range of sizes and designs with varying ranges of thicknesses and grades of materials to suit the preferences of the diver wearing the suit.
When using the suit in cold water, such as diving under ice sheets, the wearer of the suit will normally wear a thick undersuit under their drysuit. The thickness of the undersuits varies and can be selected by the user depending on the temperature of the water. Thinsulate is one the preferred fabrics for undersuits, but there has been a move in recent years aerogel material has been used to the undersuit to increase the insulating capabilities of the garment. Neoprene drysuits are constructed from a foam and rubber sheet containing small amounts of air bubbles, that provide insulation by themselves and reduce the need for an undersuit or greatly reduce the thickness needed for the under fabric.