How to choose the best undersuit for drysuit diving

28th March 2021 By Jim

There are sooo many options for layering up underneath your drysuit… how on earth do you wade through all the info and choose the best undersuit for drysuit diving?! When Maria and Kevin came to Honest HQ to go through biomap measuring for their new Fourth Element Argonaut drysuits, they also wanted some advice to help them decide which undergarments they should invest in.

The thing is, it totally depends on what kind of diving you’re doing. I sat down with Kevin and Maria, we had a cup of tea and started to chat about their diving so I could work out what undersuits would be best for them.

I turned our conversation into this very article! If you ask yourself these 5 questions, you’ll be able to narrow down your choice and find the best undersuit for drysuit diving for you.


1. Do you feel the cold?

Ah, the golden question! Some people are just naturally cold-blooded. When everyone else is enjoying the summer sun in their shorts, these guys are still feeling the cold even though they’re sitting in their hoodies!

If that sounds like you, you need to consider the best undersuit for drysuit diving very carefully. There’s nothing worse than being cold on a dive, it just spoils the whole experience and forces you to surface way sooner than you want to.

Maria considers herself to fall into this category. Her secret to success will be layering. You should aim to build up a wardrobe of undergarments rather than relying on a single undersuit to keep you warm. When you’ve got lots of items to choose from, you can pick the best combo to suit the dive.

For example, for summer dives (where the water in bonny Northumberland can top 16°c) I’ll grab my Fourth Element Xerotherm top and leggings. As the temperature starts to drop in the Autumn, the Xerotherms become my base layer and I chuck my Fourth Element Xcore Vest on top. In the middle of winter, the water temperature can bottom out at 6°c in the North Sea, or even as cold as 2°c if we’re diving in freshwater. In these more challenging conditions, I layer up with my Fourth Element Halo on top.

Having this approach makes everything super flexible and you can tailor-make your undersuit to match the conditions.

Drysuit undersuit layering

2. What type of drysuit do you have?

As I mentioned, Kevin and Maria were getting measured for their custom-fit Argonaut suits. These are made from a trilaminate material – which is essentially just a fancy waterproof bag! This type of suit is super comfy and really flexible but it doesn’t give you any thermal protection. You’ll have to carefully choose the best undersuit for drysuit diving in a trilam to make sure you stay warm, but the good news is that there’s plenty of room to layer up to get the best results.

If you dive in a neoprene suit, you’ll find that the suit itself helps to keep you nice and warm. If you don’t really get bothered by the cold, you might not need anything substantial underneath – I know a lot of divers who only wear shorts and a t-shirt underneath! When the water temperature starts to drop and you feel like you need an extra boost, you’d reach for an extra layer, right? The only thing with neoprene suits is they tend to be a bit more tight-fitting. There’s not a lot of room under there to add layers – especially if you want to add something bulky.

You also need to think about the buoyancy properties of anything you wear underneath a neoprene suit. They’re pretty floaty to start with so adding a floaty undersuit to the mix is going to mean carrying an extra couple of kilos to compensate! I think in these circumstances the Xcore range would be perfect as they’re neutrally buoyant and are just, well, amazing!


3. What type of diving are you going to be doing?

A super important factor in choosing the best undersuit for drysuit diving hinges on how often and how long you spend in the water.

If you’re a fun diver who enjoys the odd dive trip on a weekend then you may find that you don’t feel the cold as much as someone who dives regularly. The more time we spend in the water, the colder we feel as our resistance drops.

Kevin and Maria are active diving instructors. They will inevitably spend more time in the water compared to a fun diver. As a fellow Instructor, I totally get this! When I’m busy teaching students at The Fifth Point I might do 2 or 3 dives in a day (sometimes more if we’re night diving too!)

Dive pros also find themselves moving less than they would on a normal dive. When I’m concentrating on my students I spend a lot of time hovering in the same place while they’re completing their skills. And as you know, one way to warm up when you’re cold is to start moving!

Technical divers also face a similar issue. They spend hours underwater, often at extended ranges where the water temperature is colder too. To choose the best undersuit for drysuit diving on a technical dive, you’ve got to plan carefully. Being cold can slow and impair thinking plus I can’t imagine anything worse than feeling baltic while doing a deco stop knowing that I’ve got no choice but to wait it out. That would be the longest stop of my life!

Drysuit undersuit on a boat surface interval

4. What’s your budget?

I’ve been banging on about building a whole wardrobe of items so you can customise your undersuit. But let’s be honest, that’s gonna be expensive. Unless you’ve got a big budget, it’s going to be impossible to buy all the layers that you need. My advice? Build your wardrobe over time.

If you’re investing in your first undersuit, start with a good quality allrounder. The Fourth Element Arctics are a perfect example. We use them in the school at The Fifth Point and they help keep our students toasty warm all year round.

You’ll notice the Arctics come in a onesie style and a two-piece top and leggings bundle. They’re both great options, but I love the two-piece as it kinda looks like normal clothes. You can still go down the pub with these on after your dive and not get too many funny looks! Plus having separate tops and leggings will help you be more flexible with combos later on.

As soon as you’re ready, or you’re starting to feel the cold, add to your collection. Over time you’ll have the best undersuit for drysuit diving in every condition!


5. Do you want to protect the ocean with your undersuit?!

You know that we’re passionate about protecting the ocean here at The Honest Diver. I couldn’t write this article without mentioning how AMAZING the Fourth Element X-Core range is.

First of all, they perform brilliantly – all of the Honest Team wear them. And actually, we first found out about the X-Core vest when Nic was thinking about getting a heated undersuit. The guys at Fourth Element convinced her to try the X-Core and wow, it’s crazy how warm it keeps you. When they released the X-Core leggings, we were chomping at the bit to try them and they’re just as good!

But the thing we love about them most… they’re ocean positive. The X-Cores are made from 76% recycled polyester and REPREVE® – a fibre manufactured from recycled post-consumer waste like plastic bottles. You’re literally wearing trash that could have found it’s way to the sea and contributed to the 8 million tonnes of plastic that enter the ocean every single year!

On top of that, the Polartec® fabric that’s used in the range (the bit that helps keep you the toastiest) holds Blue Sign® and Oeko-Tex® certificates to prove that harmful chemicals are minimised or eliminated completely where possible and the water is treated to make sure it’s clean before it’s released from the factory.

EPIC! And the reason it scores so highly on our eco-rating!


I hope that’s helped you work out the best undersuit for drysuit diving, but if you’ve got any questions just give me a shout! We can chat over email or if you prefer we can set up a video call to go into more detail and I can actually show you the undersuits too! I’m here to help and give honest advice 🙂




5 tips to help choose the best undersuit



Jim is a PADI Master Instructor and self-confessed kit nerd. He's literally like a walking product catalogue. If you're looking for a piece of gear, but you're not sure where to start, give Jim a shout. He will find out exactly what you need, what problems you're currently experiencing and everything you hope to achieve and turn it into a solution... It's amazing! He's been diving for 15 years and an instructor for over a decade. He adores sidemount diving, we can't remember the last time we saw him in a single tank set up outside of the training tank!