Wetsuits, Drysuits & Heat Loss: The Physics Behind Why Exposure Protection Works (and Fails)
Paul Lenharr Jan 23, 2026
Wetsuits, Drysuits & Heat Loss: The Physics Behind Why Exposure Protection Works (and Fails)
Divers often choose exposure protection based on water temperature charts, personal tolerance, or whatever feels “good enough.” But warmth underwater isn’t about comfort — it’s about physics.
Water removes heat from your body 25 times faster than air. That single fact explains why exposure protection is one of the most critical systems in diving, right alongside regulators and buoyancy devices.
Understanding how wetsuits and drysuits actually work — and why they sometimes fail — makes you a safer, more capable diver.
1. Heat Loss Underwater Is Relentless
Your body loses heat underwater through four mechanisms:
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Conduction – direct heat transfer to water
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Convection – moving water stripping heat away
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Radiation – minor but constant
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Respiration – breathing cold gas
Even in “warm” water, the heat drain is continuous. Once your core temperature drops, everything degrades:
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dexterity
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reaction time
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gas consumption
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situational awareness
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decompression efficiency
Cold is not just uncomfortable — it’s a performance limiter.
2. How Wetsuits Actually Keep You Warm
Contrary to popular belief, wetsuits do not keep you dry.
They work by:
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Allowing a thin layer of water in
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Trapping that water
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Letting your body heat it
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Preventing it from flushing out
The insulation comes from neoprene, which contains gas bubbles that slow heat transfer.
Key physics points:
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Thicker neoprene = more trapped gas = better insulation
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Compression at depth reduces neoprene thickness
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Less thickness = less insulation
This is why a 7 mm suit at the surface doesn’t feel like a 7 mm suit at 80 feet.
3. Why Wetsuits Fail (Even When They “Fit”)
Wetsuits lose effectiveness when:
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water flushes through cuffs or zipper
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fit is loose in the torso or limbs
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neoprene is old and compressed
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seams leak excessively
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diver moves excessively
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thermoclines cause temperature shock
A flushing wetsuit isn’t “a little cold” — it’s a heat pump working against you.
This is why premium wetsuits use:
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anatomical paneling
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internal seals
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glued and blind-stitched seams
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high-density neoprene
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minimized zipper exposure
Details matter more than thickness alone.
4. Drysuits Change the Equation Entirely
Drysuits don’t trap water — they isolate you from it.
Insulation comes from:
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air trapped inside the suit
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undergarments that hold that air
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reduced convective heat loss
Key advantages:
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insulation remains stable at depth
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thermal control is adjustable
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less post-dive fatigue
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longer dives in colder water
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better decompression outcomes
A drysuit is not just for “cold water” — it’s for thermal consistency.
5. Undergarments Matter More Than the Drysuit Shell
The drysuit shell is just a barrier.
The warmth comes from the undergarments.
Effective undergarments:
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trap air without compressing
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wick moisture
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maintain loft under pressure
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allow movement without restriction
Cheap undergarments collapse at depth, losing insulation exactly when you need it most.
This is why shops that specialize in cold-water diving focus heavily on undergarment systems — not just suits.
6. Fit Is Physics, Not Fashion
Poor fit creates:
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air migration
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cold spots
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restricted movement
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difficulty venting gas
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buoyancy instability
A well-fitted exposure system:
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distributes insulation evenly
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supports stable trim
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reduces task loading
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improves breathing control
If a diver is fighting their suit, they’re burning energy — and heat.
7. Cold Directly Affects Decompression Safety
Cold exposure:
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reduces blood flow to extremities
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slows nitrogen elimination
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increases post-dive bubble formation
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raises CO₂ levels via shivering
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worsens narcosis and fatigue
This is why technical and scientific divers treat thermal protection as part of decompression planning — not an afterthought.
The Takeaway
Exposure protection isn’t about comfort.
It’s about heat management, performance, and safety.
When you understand:
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how heat moves underwater
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why neoprene compresses
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how flushing steals warmth
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why drysuits stabilize insulation
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how fit controls efficiency
…you stop choosing exposure gear by temperature charts alone and start choosing it by physics.
That’s why SoMD Divers focuses on well-designed wetsuits, drysuits, and undergarments — because thermal stability changes how you dive, how you decompress, and how you feel long after the dive ends.