What is a Membrane Drysuit?
A membrane drysuit is made from a special laminated fabric that is usually comprised of three layers of different materials which gives this style of suit it’s other name of a Trilaminate Drysuit. One of the advantages of a membrane suit is that the choice of materials will ultimately determine the characteristics of the suit, giving manufacturers control over the weight, abrasion resistance and cost just by modifying the materials.
Membrane suits typically use three layers:
- An outer hardwearing layer
- A waterproof butyl middle layer
- A comfortable inner layer which might incorporate some thermal characteristics
It’s not a given that a membrane suit will have three layers. It may have more, it may have less (it may even have a separate internal dry layer) but three is the norm.
Membrane drysuits have their advantages and disadvantages like anything else. The fabric provides very little protection against the cold so a diver is heavily dependent upon an additional thermal undersuit to provide thermal insulation. Whilst this might sound like a huge disadvantage compared to the thermal insulation provided by a neoprene drysuit it can prove to be very useful for a diver that dives in varying water temperatures by simply adjusting the undersuit that is worn. You can read more about undersuits in our Choosing a Diving Undersuit Guide.
Unlike neoprene, the membrane fabric is not affected by compression as you dive deeper which means the suit itself does not lose thermal insulation, thickness or buoyancy. The internal air space is easily maintained by injected or releasing air so the effect of compression and expansion there is easily rectified.
The fabric also doesn’t offer much in the way of stretch either which means the manufacturers must accommodate for movement by having excess material. If you hold up a membrane suit it is hard to imagine that it will fit properly but by the time you have crouched down in it to vent the air out it is actually quite a snug fit. How this excess material is handled can vary but you will see certain things pop up frequently:
- Telescopic Torso – This is a folded piece of fabric over the body section that allows better movement. The excess material is often controlled using a crotch strap which prevents the material from riding up. A telescopic body is only available on rear entry drysuits as the zip on a front entry suit prevents it.
- Internal Braces – Elasticated braces keep the suit pulled up, preventing uncomfortable bunching of fabric in the legs.
All this excess material creates a problem that is particularly pronounced for membrane drysuit divers. Unlike a neoprene suit which is quite snug because it stretches and provides it own level of thermal protection, a membrane suit needs an air gap between the skin and the suit for thermal garments. Unfortunately, air is buoyant in water and has a habit of moving around within a container such as a drysuit. This air migration can cause air to move to the legs and cause inverted ascents for inexperienced divers. Ankle weights can help with this problem but as you dive with a drysuit you quickly become accustomed to the migration and learn to identify the signs.
Component wise membrane drysuits don’t really differ from neoprene suits. The same valve systems, seal and boot/sock options apply across both of them but there is one difference which is the zip. Whilst the type of zips available for both is the same, there is an additional option for membrane in terms of its position.
Neoprene suits have a rear across the shoulder zip and that is the only option. At the time of writing this there were no manufacturers offering any other zip placements. On the other hand, a membrane suit has the options of a rear zip or a diagonal front zip.
Let us take a moment to talk about zip types. The traditional brass zip is the standard fit for drysuits, it does the job but it needs regular cleaning and lubricating for the zipper to run smoothly, it is stiff, can be uncomfortable to wear and is prone to damage if bent the wrong way. Generally this is fine for across the shoulders where it doesn’t bend much but you need someone else to open and close the zip for you.
Enter the front zip which does away with the reliance on someone else zipping you up but not quite closing the zip properly so you have a damp dive (always check it by the way!). Front entry suits have become much more popular but, the traditional brass zip is not the ideal solution because it is stiff, causing the suit to fold awkwardly and potentially become uncomfortable. The ultimate solution is the composite (plastic) dry zip. These zips are totally flexible, much thinner than brass zips, are lighter and require less maintenance. If you are having a made to measure suit created or are replacing a damaged zip it would be worth your while to look at the option.
We're Here to Help
Buying a drysuit is a big thing and shouldn't be entered into lightly. Ask questions, speak to other drysuit divers to get their opinion but always remember that it is there opinion about the suit they own and dive with. One diver's drysuit might not be the best option for another.
We are happy to help answer any questions you may have about the drysuits we offer. Our range covers off the shelf, customised and made to measure options and we have some very knowledgeable and experienced divers waiting to give you a hand. If you would like to visit the store to look and try on drysuits please give us a call so we can have someone ready for when you arrive.