How to choose an undersuit for drysuit diving?
Picking the best choice of undersuit or combination of layers and thicknesses for the water temperature you will be diving in will make a massive difference to your enjoyment of the dive.
Unfortunately, because there are so many variables involved there is no hard and fast rule or formula for how to choose the best undersuit as every diver and every dive is different. Things like your physical condition, body composition drysuit materials and how hard you work during a dive can all affect how tolerant you are to temperature changes. The best advice must always be considered alongside your own knowledge of how you react to different temperatures.
A Little Knowledge...
So, what keeps you warm whilst diving in a drysuit? For the most part it is the air that is sealed within your suit and to a lesser degree the materials that your drysuit and undersuit are made of. In theory, the more air you trap the better the insulation but trapped air spaces are not a divers friend. Air has a nasty habit of compressing and expanding as the pressure (depth) changes as well as being buoyant in water, so whilst the theory is that more air equals warmer the real-world practicality is that more air means more weight to compensate the buoyancy on the surface and a greater buoyancy fluctuation as you get deeper.
So, the perfect undersuit needs to be a balance between warmth, bulk, buoyancy and compression. A tall order perhaps but don’t forget that the answer doesn’t necessarily have to reside in just one product.
Going straight for the thickest undersuit for winter diving isn’t necessarily the best option. There are big advantages to opting for a combination of layers. Having a range of different thickness garments will allow you mix and match to achieve the best choice for your dive but it will also allow you to tailor your final system for best performance.
The layer in contact with your skin needs to do a particular job. Even when you are relaxed, calm and comfortable your body sweats so your undersuit needs to be able to move this moisture away from the skin to prevent you becoming damp and cold. Most undersuits use materials that are fast wicking but base layers such as the Fourth Element Drybase or J2 Baselayer are ideal as they have been specifically designed to achieve this.
Something to bear in mind is that cotton is terrible at wicking moisture. It will just get caught within the fabric, getting wetter and colder so making you wetter and colder. If you aren’t going to use or need a baselayer don’t be tempted to wear a standard cotton T-shirt instead otherwise you’ll just be making it tougher for your undersuit to its job.
Where you go from here is very much up to you but we’ll give you a bit of a guide as what as to what sort of thickness undersuit or specific product falls into certain temperature bands to give you a starting point.
For a guide on which undersuits to choose based on temperature please see our article here!