Drysuit undergarments are essential for cold water diving

Divers need to be comfortable underwater in order to enjoy themselves; comfort while diving in BC means staying warm throughout the dive. Maintaining warmth is largely dependent upon the exposure protection that divers choose. This is a critical element of cold and temperate water diving equipment.

Much is discussed in regards to drysuits that help protect divers from the elements, but a crucial piece of gear is often overlooked. The best drysuits for fit, mobility, customization and buoyancy characteristics do not provide much actual insulation for the diver. This is done primarily by the drysuit undergarments worn beneath the suit. It seems odd, then, that many divers and dive professionals pay little attention to something that has such a large impact on the enjoyment of a dive (and, ultimately, safety as well).

So what should one consider when purchasing drysuit undergarments?

Of course, warmth is the key factor, but plenty plays into how warm an undergarment truly is when you get it in the water. Something can seem and sound fantastically warm in a dive shop, but if it is not just as insulating at 20 metres than it isn’t really doing the job it is intended for. Undergarments may come as separate tops and bottoms which tend to allow more versatility and may even be used in non-diving applications; while one-piece suits are generally warmer and minimize cold spots that may occur from two pieces shifting apart. What an undergarment is made out of is also among the first things to consider. For the most part you will find undergarments made out of synthetics like fleece or Thinsulate, but occasionally wool makes an appearance. The warmest undergarments, for the coldest dives, tend to be made out of Thinsulate. However, not all Thinsulate suits are made equally.

There are several drysuit undergarments available that are rather lofty (400+ weight). These give the impression of warmth while puffed up on land. However, these must remain puffed up with air in order to maintain their warmth. This does not translate well to a diver in a drysuit under hydrostatic pressure. One would have to maintain an excessive amount of air in their drysuits in order to maintain the warmth of these garments. This can be avoided by using an undergarment that features a pre-compressed Thinsulate like that found in Santi BZ series. Even when under pressure these suits maintain their thermal properties. This means divers can dive with an appropriate amount of air in their suits, which keeps from complicating buoyancy and trim issues. It also means that one can have a more streamlined-fitting drysuit over top. The quilting incorporated by Santi prevents the internal Thinsulate from packing down to the bottoms of the legs or arms and creating cold portions of thinned out material.

There are some details that are present on some undergarments and not others that can impact the insulating quality of a suit. Below are a few of the details that can separate certain drysuit undergarments:

  • insulation underneath a zipper
  • extra wicking material at cuffs (to minimize moisture seeping up sleeves and legs)
  • a high neckline and stirrups/thumb loops to keep the garment from riding up legs and arms will all work to keep a diver more comfortable in and out of the water and contribute to overall warmth
  • built-in suspenders help keep the undergarment in place while underwater and allow divers to doff just the top of their suit
  • garment between dives for thermal regulation at the surface without having to climb all the way in and out of their exposure protection.

The relationship between undergarments and drysuits is not limited to thermal properties.

Both greatly impact a diver’s mobility in and out of the water. Stretch panels are a must for mobility, accounting for areas of the body the diver will be putting through a wide range of motion. These usually include the shoulders/armpits and waist regions of the suit. These stretch panels should be flexible, but still made out of a well-insulating material. Having these areas of the body (armpits and kidneys) exposed to cold will rapidly increase heat loss in an otherwise well-insulating garment. Having regions of folded Thinsulate that will expand or contract with movement tends to an ideal source of thermal protection in these areas of the body.

Overall fit of an undergarment is highly influential on comfort and mobility

In addition to stretch panels, the overall fit of a drysuit undergarment is highly influential on a diver’s mobility. If an undergarment is too tight or short or otherwise restrictive it will impede a diver’s ability to fully stretch out in the water and therefore potentially impair the ability to reach different parts of their body and/or perform comfortable and efficient kicks. Suits that are well-tailored are key. For divers that don’t easily fit into a custom size for various reasons, the upgrade to a custom undergarment is indescribably worthwhile. This is particularly true if one has gone to the trouble and expense of ordering a custom drysuit. No matter how well a drysuit fits, if an undergarment fits poorly a diver’s mobility will be restricted. Drysuit undergarments that are too big for a diver can bind and twist inside a drysuit and not only impede air movement in the suit, but also restrict mobility.

Mobility and air movement throughout the suit are primarily why it is best to have one adequately warm, well-fitting, moisture wicking undergarment than multiple layers. However, the initial investment in such an item can be a little daunting for new divers, so there are other options that are good, just not ideal. For those putting together something they wish to be versatile, companies like Bare and DUI offer some two piece undergarment combinations that may transfer over to other cold weather activities as well. Companies like Hollis have affordable 200 weight Thinsulate undergarments that can be matched with these options or with other moisture-wicking, insulating garments the diver may already own from other activities. These are also a great option for divers that may do some of their diving in BC, but wish to take their suit with them to more semi-tropical/temperate waters (such as California or the Eastern Seaboard of the US) or for those working in the water, particularly in the shallows.

For those looking for some additional warmth, boot liners, dry gloves and liners and Thinsulate vests may be added to undergarments. For extended dives some divers opt to employ heated undergarments, powered by an external battery canister.