Undergarments: The Unsung Heroes of Drysuit Diving
I’ve always been a warm-water diver. Most of my diving life was spent in wetsuits—until 2020, when I decided to become a cave diving instructor. That decision kicked off my mission to become a more versatile and resilient diver. Diving a drysuit requires a higher level of skill and awareness—it's not the easiest route for most divers. In this article, I’ve put together my thoughts on chosing and using undergarments, my favorite brands and some alternatives to dive-specific garments.
How it started?
During the unforgettable global pandemic, with the world on pause, I suddenly found myself with endless opportunities to dive in caves. I went from occasional cave dives to doing daily stage dives, sometimes extending my bottom times to three hours, for a beginner, that was a big leap. I also quickly picked up cave survey techniques and joined exploration projects. The more I dove, the colder I got.
Diving Cenote Cristal with several layers of Neoprene
I tried everything—adding layers, buying thicker and more expensive wetsuits—but nothing stopped me from feeling chilled almost immediately after starting a dive. The cold became a real challenge. Eventually, I would feel anxious before even entering the water, already anticipating the discomfort. On some dives, the cold even impaired my ability to think clearly and make sound decisions—I was shivering too much to focus. I was constantly cold in water considered warm—around 25°C, which is the steady temperature in most Mexican cenotes.
Let’s not even count how many times I had to pee during dives. Cold exposure increases urine production, and I’d often surface dehydrated and exhausted.
Wearing a 3mm shorty under an 8mm semi-dry suit…
By 2021, I was assisting my first Sidemount Instructor course, and that’s when I hit my limit. During one particular dive, observing a class from the sidelines, I told myself: This isn’t going to work. I need a drysuit.
Since then, I’ve owned four drysuits from two different brands and experimented with a variety of undergarments—both for warm and cold water conditions.
(If you’re curious about my review of the Seal drysuit—stay tuned for a new review coming up!)
Now, let’s talk about the stuff under the drysuit: the undergarments.
What Are Undergarments?
Think of undergarments as cozy pajamas. The drysuit is not the only piece of gear in charge of keeping you dry, the undergarments are also partly responsible for moisture control inside the suit and, of course, are meant to control temperature. Bonus: they also influence your buoyancy and trim, which you can use to your advantage.
Undergarments typically fall into two categories:
Base Layers: usually an underrated set of thin clothing intended to be worn under the thermal suit as a first layer.
Undersuits: these are also called thermal suits or undergarment, thicker insulation garments that keep us warm.
Base Layer
This is a thinner layer worn closest to your skin. Its main job is moisture management—pulling sweat away from your body to help keep you dry. Being dry and being warm are intricately related. When sweat collects inside the suit and cools down, it can rapidly chill you. A good base layer prevents that by wicking moisture outward.
Base layers also provide additional insulation. Depending on water temperature, you can choose thin or thicker base layers to add warmth without changing your main thermal garment. This is especially helpful when teaching. On active dives with a lot of movement, I rarely get cold and can wear a lighter layer. But on long exploration dives—especially with a DPV, when I move less and stay in the water for many hours—I opt for a thicker base layer to stay comfortable. On some occasions I use a base layer, an intermediate layer top, and then the undersuit. The idea is to keep the core warm.
Me getting ready for a long exploration dive at Vanilla Farm with Jack Cleary and our support team.
What I Use as Base Layer
When I first started drysuit diving, I grabbed a pair of cold-weather running pants and a top from Decathlon. It was all I could find and afford at the time, and surprisingly, it worked very well. Cold-weather sportswear is often sweat-wicking like dive clothes, but it may behave differently in the water—especially in terms of buoyancy.
A key feature in both base layers and undergarments is their buoyancy. Thicker fabrics, usually, float more, which means there’s a lot of clever engineering behind dive-specific gear to balance warmth and neutral buoyancy.
Since then, I’ve expanded my kit:
Fourth Element Xerotherm Top: My go-to for extra warmth. It’s noticeably thicker than my original running top and adds buoyancy to my upper body—a great match when diving with twin tanks. I sometimes add this layer as intermediate when I need extra warmth, for this reason I have sized up, so I can wear it on top of the thin Decathlon top.
Odlo Merino Wool Base Layers: Odlo is a high-end running brand, and their merino wool layers are fantastic. They’re thin, stretchy, and made from high-quality materials. I use them as a first base layer in cold water (sometimes layering on a second base and a main suit). Merino wool wicks moisture efficiently and is naturally breathable. It’s also great during surface intervals—you can strip off the top layers and still stay warm in your drysuit when air temps are fresh, even in a breeze, and you won’t be overheating in the sun.
Me in my Odlo top as base layer during cold water diving project in Alaska.
Kari Traa, a premium ski and winter clothing brand from Norway. One of their merino wool tops quickly became a favorite base layer.
Vintage Kari Traa top as second base layer to dive Alaska.
❗ Never use cotton. It doesn’t wick moisture, and once wet, it makes you cold. Even though cotton feels nice on the skin, it’s a big no-no for diving undergarments. Wearing a hoodie, or jeans as undergarments is something I DO NOT recommend, unless you have forgotten all your clothes at home (it happens!). Wearing these types of clothes for technical diving doesn’t give a very professional image either. I know, diving gear is expensive, but there are ways around it (such as Decathlon running clothes).
Why Base Layers Matter
Choosing the right base layer isn’t just about warmth. Undergarments also provide physical protection. If you wear only a thin layer under your drysuit, the fabric can squeeze your skin uncomfortably during a dive. I’ve experienced this firsthand. Once, I skipped wearing the undersuit and went with only a thin set, this caused my inlet valve to press against my chest too hard, leaving a red, swollen valve-shaped squeeze for days. (Yes, it was funny—but also painful!)
For that reason, I make sure to use proper dive undergarments to avoid skin compression. In cold water (4 degrees or so!) I found that the thin fabric folds in base layers became painful once in the water, a thicker base layer prevents this from happening.
I don’t recommend using lycra skins. They tend to hold sweat against your skin, opposite of what we want, and often retain smells. Dive-specific garments often have antibacterial properties and are designed for better moisture control.
Another important feature of dive undergarments is how they perform in case of leaks. High-quality garments can wick moisture outward even if a bit of water gets in, making leaks unnoticeable. In the case of a full flood, some fabrics mimic the thermal function of a wetsuit—trapping a layer of water that helps retain body heat.
Is Choosing Undergarments a Science? Yes.
That’s why many drysuit and undergarment manufacturers offer detailed guides on their websites. They help divers pick the right configuration based on temperature, dive duration, movement level, and personal comfort. Some have smart charts or very detailed recommendations for the temperatures they’re supposed to be used in. When researching undergarments, its a great idea to spend some time reading about the characteristics of each piece.
For me personally, the top base layer is non-negotiable. I’m sensitive to the feel of fabric on my skin, so I always choose a comfortable piece to wear underneath my main thermal suit. My current favorite undergarment is made from a special type of foam—not fabric—and while it performs beautifully, it’s not soft to the touch. That makes my base layer even more essential.
On the bottom though, I’m ok to wear leggings that I put on at home in the morning, I do not necessarily wear base layer pants, mainly because I don’t get cold in my legs. Unless I am diving cold water like I did in Alaska, with water 6 degrees.
One Last Tip on Base Layers (for Students and New Drysuit Divers)
Many students show up to class with just a base layer, thinking it’s enough because water is warm in Mexico, but that’s a beginners mistake.
Even in “warm” caves, the water feels colder than it is. You’re not in the sun. You’re in a dark, thermally consistent environment, doing multiple dives or long sessions requiring a lot of energy. You’ll get cold eventually.
Gas consumption is directly affected by temperature. Getting chilly is definitely going to increase your breathing rate.
Plus, if you’re used to diving with thick undergarments and suddenly switch to just a base layer, you’ll have trouble managing your drysuit’s gas bubble and you may be overweighted without even if you haven’t added any additional weight. The suit may fold in odd places, gas won’t vent properly, and your trim will shift unpredictably. Full undergarments provide structure and occupy the space in the suit, making gas travel more evenly and controlled, making buoyancy and movement more manageable and smooth. And don’t forget proper socks! Having empty foot pockets or boots will allow a lot of gas to lodge there, causing floaty feet. Fill the space with thick hiking socks and you’ll notice a difference.
Undersuits (Thermals or Undergarments)
Undergarments for drysuit diving are often rated similarly to winter sports gear. The most common measurement is GSM—grams per square meter—which refers to the weight (and indirectly, the thickness) of the material. You might recognize the term from paper weight as well. In diving, a higher GSM means a thicker, more insulating undersuit.
Undersuits, generally, range anywhere from 80 GSM to 600 GSM. The higher the number, the warmer the garment. Many can be layered, giving you flexibility across a range of temperatures.
My very first undergarment was a 150 DuoTherm men’s jumpsuit from DUI. And let me tell you—undergarments may not be flattering, but no one’s judging your fashion sense underwater. Like pajamas, they do the job, keep us warm and cozy, and that’s what matters.
Later on, I upgraded to a women’s 300 DuoTherm jumpsuit, also from DUI. It was warm and comfortable but bulky. I couldn’t stay in it during surface intervals without overheating.
That’s why I was so impressed when I got my current undergarment set. It’s not available on the market, but it was sent to me by Seal Drysuits, Seawolf currently produces the orignal version of it using a unique non-compressing foam-like fabric that traps air between the body and the drysuit—essentially creating an insulating buffer of warm gas around you.
The Seal undergarment is not available on the market, unfortunately, because this is a great garment.
I own a two-layer set, which can be worn together or separately. The thin layer is roughly equivalent to a 300 GSM garment but feels lighter than a 3mm wetsuit. The thick one compares to 400 or 500 GSM, but I rarely wear it—it's simply too warm for most of my diving. If you wear them together you’re set for cold water.
I usually don’t wear a base layer on my legs with this system. I stick to my usual leggings underneath the one-piece suit, mainly because I dislike how the inner fabric feels on my skin. I do not wear the undersuit without the leggings. On top, I wear a long-sleeve base layer—either a thin Decathlon running fleece or a Fourth Element Xerotherm. I’ve also used a The North Face fleece on occasion and found it worked well.
There’s a lot of research and innovation behind high-performance undergarments for drysuit diving. While the drysuit itself is the main player, a good undersuit makes a huge difference in staying dry, warm, and comfortable during long or technical dives.
Some companies have developed proprietary materials; others are creating gear from recycled fibers like polyester, or adapting high-performance materials from extreme sports like alpine climbing.
Here are some common materials you’ll run into:
Climashield: A filament interlocking technology known for retaining warmth even in humid conditions.
Polartec: The inventors of fleece, this fabric traps air to provide insulation while preventing overheating.
Thinsulate: A densely packed yet lightweight fiber that offers impressive warmth with less bulk.
Alternative Setups for Lighter Dives
Sometimes I swap out a full undersuit for separate pants and a top, especially when guiding cavern dives. These dives are usually about an hour long, and I often need to drive during the surface interval to a second location. Efficiency is key—no one wants to be wrestling with garments in a hot car.
That’s where the Fourth Element Arctic leggings and Xerotherm long-sleeve top come in. They're lightweight, easy to put on and take off, and provide just the right amount of insulation for short dives.
Cold Water for a Mexican
All of this works great in warm water, but transitioning to cold water diving was a whole new learning curve for me.
My first cold water experience was in Alaska, where I joined the Sunfish team to explore and document submerged caves in Southeast Alaska. Months of preparation went into this expedition. I was fortunate and grateful to have been sent a full set of Santi cold water gear, including heated undergarments, dry gloves, and a thermovalve.
After a dive in Southeast Alaska on the Sidewinder rebreather
Before heading out, I practiced with the setup on several dives to get comfortable with both the gear and the procedures.
For the dives in Alaska, I wore my Odlo merino wool base layer—this wool layer is warmer and thinner than fleece, which helped because my drysuit and undersuit were made to measure, leaving little room for bulky layers. Over the Odlo set I wore the Santi 400BZ heated undergarment, powered by a Seaya battery canister with a dual output: one for my primary light, and one for the heating system.
The heated gloves connected to the suit’s wiring through the sleeves. On top, I used Santi dry gloves mounted on an Ultima ring system—my chosen system for my Seal Drysuit. Installing the dry gloves requires four hands (it’s a bit of a juggling act), but once they’re on, they’re incredibly easy to use, just like removing the lid of a Tupperware. Having the Santi heated gloves was a blessing because fingers are the first thing that suffers when you begin to feel cold.
The face does not describe how much I love the undersuit, but how difficult it was to get ready in the cold while sweating!
How to Dive with a Heated Undersuit?
That depends on the dive culture, objectives, and the complexity of the dive.
In Alaska, I turned the heating on at the start of the dive. I’d usually get about an hour of heating from the battery, and sometimes managed to stretch the dive another hour without heating. Water temps were around 6°C, and the air was the same—so there was no temperature shock. These were shallow, non-demanding dives with no decompression obligations (the demanding part was actually getting ready to dive!). My logic was simple: heating = comfort = better focus.
But everything changed the following year.
I traveled to Poland for training at Lake Hancza with Jacek Konikowski. His philosophy was the opposite: "You can’t avoid being cold in cold water."
Me and Jacek diving in Poland
Honestly, if he’d told me that beforehand, I probably wouldn’t have gone.
The water in Poland was just 4°C—only two degrees colder than Alaska, but it felt significantly colder— the air was 25°C. That 17-degree difference created a brutal thermal shock.
Jacek’s method was to keep heating off during the dive, and only switch it on during the ascent to our first decompression stop. That way, if heating failed, your body wouldn’t suddenly go from warm to cold mid-deco, which could impact off-gassing and overall safety.
At first, I didn’t think I could do it. Mentally, the fear of being cold was a huge block. But I had committed to this training, and Jacek provided the guidance, patience, and support I needed. I trusted him completely. His presence was calm, validating, and confidence-boosting.
My previous training and skills definitely helped, but this was still the biggest mental barrier I’ve ever faced in diving.
Diving Hancza Lake during my MOD 3 training with Jacek on the Kiss Sidewinder
Jacek also taught me something I still carry with me:
"To know how much cold you can take, you have to dive without heating."
You need to learn your personal limits, you need to experience cold to understand yourself and how cold is too cold for you. Only once you know your baseline tolerance can you truly appreciate the comfort that heating brings—and use it wisely as well as plan dives that are within your level of tolerance. Progressive penetration also applies here, extend dives little by little to get used to it.
During that course, I went from doubting whether I could handle cold water at all, to completing MOD3-level dives with a full flood in one sleeve and glove at 80 meters. I still had to do my deco stops and perform the required skills, soaking wet, and freezing. But I did it. I earned every millimeter of that certification card, and I couldn’t have done it without trusting my instructor completely. As I said before, having the right undergarment saved the dive, the day and the trip. If I had not completed the skills on that dive, I would not have been able to finish the certification.
Me after finishing MOD 3 on the KISS Sidewinder in Poland
We Haven’t Talked About Socks!
Let’s not forget foot insulation—it’s crucial.
On cold water trips, I’ve tried several combinations:
DTEK fleece socks: Warm but floaty (I sometimes lend them to students with heavy legs to balance out trim).
Thin SmartWool socks
Long wool ski socks
In Poland, I wore three layers; in Alaska, two were enough.
Feet don’t require dexterity like hands do, so I’ve found that a little cold on the toes is tolerable. But don’t underestimate the importance of keeping your feet warm—especially on long or decompression-heavy dives.
Now the stinky side of diving!
First off, most people don’t wash their undersuit often—and some, not at all. That’s a personal choice. My go-to undersuit is made from a foam-based material that doesn’t retain odors, another reason why I love it so much, it’s always been smell-free. That said, I definitely give it a wash whenever I’ve had a pee valve leak—which, let’s be honest, happens at least once a year!
My base layers, however, get washed almost every day. I love slipping into a clean, fluffy set that smells like my favorite fabric softener. It's a small comfort that makes a big difference.
After a dive, I lay my clothes out in the sun to dry while I pack up my truck. Thanks to the Mexican heat, they sometimes dry completely before I even leave the parking lot. Sun-drying helps air them out and keeps unpleasant odors from sticking to the fabric. There is also a product called Febreeze, I have used this in the past during the periods of the year when humidity is very high (hurricane season!), sometimes clothes don’t dry very well in our climate, a little help goes a long way!
One thing I’ve noticed is that diving-specific garments tend to stay fresher than non-diving sportswear. In my experience, the stinkiest layers are usually the ones not designed for diving. Maybe it's the fabric, or maybe it's the engineering—but it's something to keep in mind when choosing (and washing) your gear.
A few last tips for everyone who is thinking of doing drysuit diving in the tropics:
Always get dressed in the shade, it may not seem like it but a little sweat will chill you as soon as you get in the water.
Don’t wear your undergarments until you’ve assembled the gear, taken your tanks down to the water, done the briefing, etc. Same here, a little effort means sweating, and we don’t want that!
If you’re doing consecutive dives and you tend to sweat a lot, bring a spare base layer to start the second dive dry, it can go a long way!
Of course, this might just be my personal experience— I’d love to hear yours!
What do you use? How do you care for it? Any favorites— or extra tips to share?
Feel free to reach out with questions, comments, or your own undergarment stories.
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