Membrane and Trilaminate dry suits are made from thin materials, and thus by themselves have little thermal insulation. They are commonly made of vulcanized rubber, or laminated layers of nylon and butyl rubber, this is why they are also known as Tri-Laminate drysuits. Membrane dry suits typically do not stretch, so they need to be made oversized to allow flexibility at the joints through the wearer's range of motion. This makes membrane dry suits easy to put on and get off, provides a great range of motion for the wearer, and makes them comfortable to wear for long periods, as the wearer does not have to pull against rubber elasticity.
To stay warm in a membrane suit, the wearer must wear an insulating Undersuit, today typically made with polyester or other synthetic fibre batting.
Polyester and other synthetics are preferred over natural materials, since synthetic materials have better insulating properties when damp or wet from sweat, seepage, or a leak.
(Except for wool, which is an effective insulator when damp, albeit bulky.) Northern Diver have a large range of under garments available which include a range of thicknesses, from the thinner Rash Vests and Thermalskin to the more heavy duty Metalux range.
Membrane dry suits may also be made of a waterproof and breathable material to enable comfortable wear when out of the water for long periods of time. Sailors and Boaters who intend to stay out of the water prefer this type of suit. This type of suit is also supplied to the majority of Fire and Rescue services around the UK by Northern Diver.