Our Advice: Choose primary material for balancing durability against weight. Choose a breathable laminate if you expect a lot of surface exertion. Use oval replaceable wrist seals and replaceable neck seal. Definitely get a pee valve and left and right thigh pockets with integrated D-ring.
Why buy a drysuit? How does a drysuit work?
Drysuits provide both thermal protection (when paired with undergarments) and backup buoyancy control. The best wetsuit will still conduct heat away from the body in anything less than body-temperature water, so even in tropical water a drysuit is necessary for longer dives. In cold water a drysuit provides a much more comfortable temperature than a wetsuit for every length of dive.
Drysuits keep you dry as they are a single piece made out of waterproof material with waterproof seals at the wrists and neck. The airspace between the drysuit and your body will compress with depth causing the drysuit to constrict around your body in a squeeze so it is necessary to equalise the internal pressure using an inflation valve on descent and an exhaust valve on ascent.
Once you have an effective and equalised airspace around your body then undergarments provide thermal protection against the cold.
What is the best drysuit material?
High quality drysuits are of the “shell” type which have these advantages:
- No buoyancy change with depth,
- No thermal change with depth,
- Lightweight and compact for storage and travel,
- Dries quickly,
- Easy to find leaks, and
- Allow full range of limb motion.
Drysuit materials have two separate parts: primary material and laminate/membrane.
In deciding on your primary material it is necessary to balance weight, durability, flexibility, and comfort:
- Cordura polyester: very heavy weight, very durable, not flexible or comfortable.
- Softdura polyester: heavy weight, durable, flexible, and comfortable.
- Kevlar: light weight, durable, flexible, and comfortable.
- Polyamide: very light weight, durable, very flexible, and comfortable.
The most common laminate/membrane is butyl rubber but there are also waterproof breathable polyurethane laminates (eg Dermizax), which keep you dry from water but allows water vapour to exit.
What about neoprene drysuits?
We have not talked about neoprene in this overview because it is not a recommended material for drysuits. Neoprene has a number of disadvantages:
- Thermal protection weakens with depth as the neoprene becomes crushed,
- Requires a lot of weight to descend and maintain shallow stops,
- Causes overweighting at depth as the neoprene becomes crushed,
- Difficult to find leaks,
- Heavy and bulky for travel,
- Dries slowly,
- Less flexibility for limb movements.
Historically neoprene had the advantage of being more difficult to puncture than shell suits, but this is no longer true with newer materials. Now the only benefit of neoprene drysuits is that they are cheaper.
Silicon v latex drysuit seals
Silicon is lightweight, flexible, and stretches well for ease of dressing. Silicon stretches to mould snugly to your body, making a good waterproof seal. The disadvantage of silicon is that it punctures relatively easily out of the water, a problem that is easily mitigated using correct handling, replaceable seals, and carrying a spare. You are unlikely to puncture a seal underwater since the drysuit material compresses around and protects the seals.
Latex is the heavy duty option and is less vulnerable to damage. There is not much stretch and it is more difficult for dressing, usually requiring sex lube or unperfumed talcum powder for help. Latex relies on a tight fit to make a waterproof seal that can feel too tight and uncomfortable. Latex does still tear, so replaceable seals and carrying a spare are recommended.
Until recently most seals were glued directly to the drysuit and required sending the whole drysuit to a specialist maintenance centre for replacements. There are now very effective replaceable seal options available which allow you to replace a broken seal in a few minutes on the boat without tools. Replaceable seals are slightly more expensive as an upfront cost, but will pay for themselves many times over the life of the drysuit. Replaceable seals will also allow you to change between silicon and latex as needed.
Replaceable seals rely on a hard ring system that comes in either circle or oval options. The oval option fits the shape of your wrist better for minimal interference with the use of your arms.
All drysuits will come with an inflation valve located on the chest. Higher quality inflation valves will turn through 360 degrees without coming unscrewed, which is important to comfortably accommodate different low pressure inflation hose lengths and different equipment rigging (e.g. to use for both sidemount and backmount configurations).
A low pressure nipple cover is useful in case you need to disconnect the low pressure inflator hose underwater (e.g. to deploy an SMB or hand-off a stage cylinder), without letting water in through the uncovered port.
You will need one dump valve on your non-dominant shoulder (usually left) so that you can release gas by lifting your non-dominant arm and control the dump valve with your dominant arm. The dump valve should have adjustable sensitivity between full manual control and automatic release.
Do you need ankle dump valves on a drysuit? Some manufacturers pander to the fears of new drysuit divers by adding ankle dump valve. These either cause unwanted gas dumps if set to automatic release or, conversely, are set to manual but are too far away to reach if needing to dump gas trapped in the feet and legs to avoid an uncontrolled ascent. Such fears are misconceived and easily addressed with the most basic drysuit training and experience.
Elastic suspenders and crotch strap
A properly fitting drysuit will be longer than you are to allow for movement in the hips and joints (known as “telescoping”). Elastic suspenders and crotch strap keep the extra length around the hips tight and clean while still allowing the necessary range of movement. Elastic suspenders are also used to keep the drysuit half-dressed on the surface.
Keeping your rigging clear and unobstructed requires that most accessories are put away in a thigh pocket. It is difficult to manage your equipment by feel in an emergency if there are finger spools and backup lights dangling everywhere and clogging up your d-rings.
A good drysuit will have both left and right thigh pockets with integrated d-rings for attaching equipment. Anything in your pocket not secured to a d-ring will be lost when you pull out your equipment.
Boots vs socks
Light built-in boots are robust and hard to damage, they are the preferred solution for most applications. Dry-socks are easily damaged and require you to wear external boots or closed foot fins. For either option, 3mm | 0.118in crushed neoprene is the best option, being soft and comfortable and not changing buoyancy and thermal characteristics much with depth (which does happen with 5mm | 0.197in neoprene).
Front-zipper vs back-zipper
Front-zipper design allows the user to don the suit without assistance and are preferred over back-zipper designs. Both front and back-zipper designs should also include a cover flap to protect the zipper from sand and dirt, as well as preventing equipment from rubbing against the zipper teeth.
Plastic vs brass zipper
Modern polyurethane zippers are not easily damaged and maintain a smooth action over time (without degradation and tearing of surrounding material which occurs with the old style brass zippers).
A plastic t-bar slider allows for ease of gripping in gloves or mittens.
Deciding between unbalanced vs balanced pee valves. Balanced pee valves equalise the pressure difference between the valve system and the ambient water pressure, avoiding a squeeze.
A good pee valve will have a check valve to avoid reverse flow of outside water into the system (which can otherwise cause extreme discomfort and urinary tract infections).
The pee valve is usually located on an inner thigh to avoid catching on equipment or the environment. The urination tube can be cut to length depending on the diver’s personal preference for routing up the leg directly to the catheter/she-pee or routing up the leg and down the stomach.
Pee valves are essential for comfort especially as your dives become longer.
Shell-type drysuits keep you dry not warm. They do not offer thermal protection on their own and you will require separate undergarments suitable for the water temperature.
Undergarments keep the diver warm by providing a layer of insulation in the air space between the diver’s body and the drysuit.
Undergarments are measured in weight using either of the two terms - grams or weight. A 200g undergarment is also referred to as a 200 weight (Wt) undergarment. This weight is a measure of grams of fabric per square meter. The heavier the undergarment, the warmer it is considered.
Undergarments work best when layering is used. A thin base layer against the skin acts as a wick to remove sweat and keep the main heavier layer dry. Cotton is not suitable as a base layer because it absorbs and retains sweat prematurely chilling the diver. Base layers should be polypropylene or a variant of this type of thin fabric.
How to make sure a drysuit fits properly
A drysuit which is too small will be uncomfortable and restrict range of movement. A drysuit which is too large will be uncomfortable, may require extra weight to achieve neutral buoyancy, and will be harder to manage underwater.
To test whether a drysuit fits properly, perform the following test in the undergarments you will wear with the drysuit:
- Raise your arms as high as you can above your head, one at a time, then both together;
- Touch the back of your neck (as if grabbing the cylinder valve) with each hand, then with both hands at the same time;
- With feet flat on the floor and shoulder width apart squat down, bending hips and knees, until resting on your haunches;
- Touch your toes with both hands, bending at the waist;
- Kneel down with one leg raised as if in a lunge, try with each leg; and
- Stand with legs at twice shoulder width apart to make sure the crotch is the right height (if too low then the movement will be restricted).
If any of these movements are restricted then the drysuit is too small.
If during these movements there remains excessive folds in the part of the drysuit being extended then the drysuit may be too large while in those undergarments.
Drysuits are more forgiving then wetsuits when they are too large. Once in the water then compression of the air space will pull a drysuit in close to the undergarments. Usually a diver will own a single drysuit used with a mix of light and heavy undergarments, and accepts there will be some excess bagginess with the lighter undergarments.