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Scuba Diving: Choosing A Dry Suit

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Scuba Diving: Choosing A Dry Suit by John Hewitt

A suit to use in cold conditions is a major investment for most divers. You are not just investing in keeping dry but also in keeping warm. To do this it must fit well with seals that are efficient at the neck and wrists.

Dry suits can be split into two main categories:

  • Neoprene
  • Membrane

The former keeps you warm due to the thickness of the foam although the foam does compress during descent becoming thinner the deeper you go. As it becomes thinner it also becomes less buoyant so air needs to be put into the suit to compensate for this. A membrane suit is usually made from a trilaminate material and is purely for keeping the water out so an undersuit has to be worn for warmth. As you descend, the air in your suit becomes compressed and seems to shrink -this is known as suit squeeze- so air needs to be put in to maintain neutral buoyancy and also to prevent "squeeze".

The air added to the suit warms up by body heat and acts as an extra insulation layer, this effect is reduced the more the suit is compressed. Bear in mind that with a neoprene suit you need to counteract the effect of squeeze AND the material compressing.

There are a couple of types of material that blur the boundaries between membrane and neoprene;- crushed and compressed neoprene. These have the toughness of neoprene but without the tendency for the suit material to alter it's buoyancy during the dive. Usually more expensive than standard neoprene or trilaminate suits.

Seals: These can be made of neoprene or latex rubber. Latex tends to be more watertight but also more fragile while neoprene tends to be robust and warmer on the wrists but often leaves a bit of a damp wrist. If you have sinewy or particularly thin wrists then latex seals are probably your best choice. Latex are usually fitted to membrane suits and neoprene to neoprene though vice versa is possible.

Valves: You need valves in a dry suit to maintain constant volume and so control your neutral buoyancy. Inflator valves are usually a simple push button type located at a convenient place on the suit, mid chest being the most popular position. These have a direct feed hose commonly from the diver's main supply cylinder though some divers carry a small cylinder dedicated to suit inflation. Deflation or dump valves come in two types;- manual and auto. The manual is a simple flap valve and is usually situated on the wrist with a simple raise of the hand to dump. The auto or to give it it's Sunday name the constant volume dump is a spring loaded adjustable valve usually located on the upper arm or shoulder.

Zips: The entry to most dry suits is closed by a waterproof zip commonly across the shoulders but, sometimes diagonally across the chest. The latter allowing you to don the suit and seal it yourself. A growing feature now in dry suits is a pair of braces. This allows the suit to be a bit longer in the body to allow for movement yet reduces the low hanging crotch so often seen on older style dry suits. Most dry suit manufacturers will make a made to measure for the same price as an off the peg so make sure your suit fits as this represents a major investment in your diving comfort.

Copyright 2006 John Hewitt is a Padi and BS-AC instructor, One of the original members of Selby Aquanauts and CEO of Red Hat Diving. His web site is

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