How Is Flexibility and Warmth Possible In A Wetsuit?

The ISURUS Wetsuit Paradox: How Can A Wetsuit Be Both Incredibly Warm and Amazingly Flexible?

You've read the reviews, maybe you've had the experience yourself - ISURUS wetsuits are renowned for being amazingly flexible, but incredibly warm at the same time. Surfers who've not tried our wetsuits themselves find it hard to believe, but it's true! 

This article goes into more detail than ever into one of the main things that make this possible:

Bubbles.

ISURUS uses Yamamoto Limestone-based Neoprene #39 & #40 in all of our wetsuits. We will not compromise on this quality, whilst we are not tied to Yamamoto, we have not found any material that's even remotely comparable in performance for surfing wetsuits. 

So how does the Yamamoto Limestone Neoprene resist the cold so effectively, yet remain so flexible?

It's all down to the density of the fabric.  To be more specific, the process that Yamamoto use to manufacture their Limestone Neoprene results in the formation of thousands of individual microscopic bubbles filled with Nitrogen.  This gas has 24 times more thermal insulation than water!  

The dense-looking Neoprene you're wearing to surf is actually filled with thousands of microscopic bubbles protecting you from the cold. Oil-based Neoprene also contains bubbles, but these bubbles are far larger, and they often inter-connect to each other, as you can see from the comparison image below.

This connection not only allows water to enter into the material, but traps it.  This water-logging results in the fabric having far worse thermal properties. It also makes your oil-based wetsuit much heavier and harder to paddle with.  This tires you out faster.

In the image above there is a hair which is 0.1mm thick on the left hand side of the image which gives a sense of scale. The bubbles in both the oil-based Neoprene (top) and the Yamamoto Limestone-based Neoprene (below) are both microscopic in size, but you can see that in the oil-based Neoprene:

1. The bubbles are far larger
2. Many of them are connected

The comparison wetsuit is a $500 USD high-end wetsuit, and the bubbles are 10-100 times larger than the Yamamoto material. 

The smaller, closed-cell, independent bubbles in the Yamamoto material have a huge impact on the thermal properties as you can see in the images below. Firstly, let's look at a visual representation of the oil-based Neoprene in air:

The next graphic shows what happens when the material comes into contact with water. You can see that the wetsuit material "fills up". This is why oil-based wetsuits can feel so heavy during your session, it's actually filling up with water at a cellular level.  

As you'll realise from how long an oil-based wetsuit takes to dry outside of water, the water doesn't simply "drain out" - it gets trapped inside these gaps and continues to get heavier and more water-logged. 

Water removes your body heat 24 times faster than the nitrogen bubbles in the Yamamoto Neoprene which explains how the fabric can have such different levels of thermal insulation.

Let's compare this to the Yamamoto fabric. You can immediately see that there are far more cells in the material and that they are "closed".  This restricts water ingress and ensures a much stronger seal against cold water.

The image above is simplified and only shows 5 levels of cells for the Yamamoto compared to 4 levels for the comparison Neoprene, but you can see from the first image that there are actually 10-100 times more cells in the Yamamoto Neoprene.

The image below illustrates what happens when the Yamamoto Limestone Neoprene is submerged in water:

The Yamamoto #39 acts like a barrier, restricting water ingress at a cellular level, and protecting your body warmth (and the fish!). These cells that are the width of a hair are what is protecting your body heat when you surf in the ocean.

How does nitrogen impact the warmth?

To understand insulation and warmth, imagine the path heat must take to escape from your body, through the wetsuit, to the cold water. Heat can move via conduction, convection, and sometimes radiation (though in water the first two dominate). Gas (like nitrogen) is a much worse conductor of heat than water or solid rubber, so by embedding many small gas pockets, we slow down heat transfer.

1. Low thermal conductivity of gas vs liquid/solid

   • Nitrogen (or gas in general) has far lower thermal conductivity than water or solid rubber. This means a gas pocket is a kind of “thermal break.”

   • The smaller and more numerous the gas pockets (i.e. microcells), the more “breaks” in the heat-flow pathway, forcing heat to zigzag through the solid rubber walls - increasing the effective thermal resistance.

2. Minimized convection inside the pores

   • If the bubbles are closed and extremely small, you avoid internal convection of the gas. (If they were larger or interconnected, gas might circulate slightly inside a bubble, carrying heat). Closed-cell structure suppresses this, making the gas stay put and act like a static insulator.

   • Because the cells are independent, there’s no pathway for fluid (water or gas) to move from one bubble to another, so there’s no internal convection chain.

3. Reduced water ingress / water trapping

   • If water penetrates the foam, it replaces the gas (or partially fills pores) with water, which is a much better conductor of heat. That dramatically reduces insulation.

   • By keeping water out, you preserve the insulating effect.

   • Also, less water uptake means less “latent cooling” (i.e. heat is not spent just warming up the entrained water).

4. Thinner foam → less “dead volume”

   • Because the foam is more efficient per unit thickness, you can use less thickness (i.e. a thinner wetsuit) for the same warmth. That helps with flexibility and reduces bulk, which otherwise would conflict with mobility.

5. Stable insulation across pressure changes

   • When you dive or compress neoprene to some degree (or under dynamic loads), the closed-cell structure helps maintain gas presence in cells vs letting them collapse or leak. That helps maintain insulation even under strain or compression.

In short:the nitrogen microbubbles act like many little “insulating air pockets,” but better because they’re closed, uniform, and filled with inert gas - giving you high thermal resistance with minimal thickness.

How does this impact the flexibility of the wetsuit?

This is where the “paradox” becomes interesting. Warmth and flexibility often conflict (thicker = stiffer). But the microcell structure helps in several ways:

1. Lower density → lower stiffness (elastic modulus)

   • If you have more gas and less solid rubber per volume, the overall density is lower. A lower density foam is generally more compliant (softer) under strain, meaning less resistance to bending or stretching.

   • Yamamoto talks about a “low elastic modulus” (i.e. easy to deform) as a trait of their materials. 

2. Uniform microstructure / minimal voids

   • Because the bubbles are very small and uniformly dispersed, there’s less “weak” spots or local stress concentrations. The stress of bending/stretching gets distributed more evenly.

   • In less optimized foam, larger or uneven voids/bubbles can lead to local buckling or collapse zones when you bend, which feel stiffer or even harsh.

3. “Cell memory” and recovery behavior

   • The idea of cell memory is that after you stretch or deform the foam, the microcells tend to push back to their original shape. That helps the suit snap back rather than stay stretched out or saggy. This helps the suit hold its shape over time. 

   • Good recovery behavior is crucial because if parts of the suit stay deformed after paddling (say around shoulders or knees), they’ll lose contact, wriggle, or let water in.

4. Reduced material mass to be deformed

   • Because you need less solid rubber (thanks to the bubbles doing insulation work), there’s less “bulk” resisting motion. The foam is lighter, so when you move (bend your arms, twist your torso) you’re not battling against heavy stiff rubber.

   • That also reduces fatigue over long sessions.

5. Multi-directional stretch and elasticity

   • High-performance neoprenes often aim for as near isotropic (multi-directional) stretch as possible. A fine microcell structure allows better balancing of stiffness in different directions.

   • If the foam is engineered so that the rubber “webs” between the bubbles are thin and uniformly oriented, you can get good stretch along and across fibers without stiffness in one direction dominating.

6. Mitigated stress concentration under bending

   • In bending or twisting, the foam layers undergo compression on one side and tension on the other. Uniform microcells help avoid local collapse or buckling in compressed layers.

   • Bubbles can act as micro “hinges” or flex points as long as their walls are thin and resilient - helping the foam conform locally.

So, the microcell structure helps reduce the “bulk penalty” of insulation, letting you maintain both warmth and mobility.

What other benefits are associated with this cell structure?

• Better durability / resistance to damage propagation

  • Because the cells are independent, a small cut or nick doesn’t propagate as easily (i.e. it doesn’t open up a cascade of connected pores). Test confirm that Yamamoto’s closed cell ratio (93 %+) is significantly higher than many petroleum neoprenes (60–70 %)

  • This helps maintain both insulation and structural integrity over many sessions.

• Lower water absorption & faster drying

  • Less water penetration means the suit doesn’t get waterlogged (which would degrade warmth, add weight, slow paddling).

  • Faster drying means less time between sessions, less thermal “cost” to dry it, and less time cold after you get out of the water.

• Better “fit” and less flushing

  • Because the foam is flexible and conforms better, the suit can maintain better contact with the skin, reducing water flushing (cold exchange between inner and external water).

  • Reduced flushing helps preserve a micro-layer of warmer water near your body (a “heat buffer”).

• Buoyancy / reduced drag penalty

  • Because the foam is lighter and remains less waterlogged, the wetsuit contributes less drag and weight penalty. This helps reduce fatigue and energy loss during paddling.

• Stability of insulation under compression

  • Some wetsuit zones (knees, elbows) are compressed or flexed a lot. The closed-cell nitrogen bubbles are more stable under mechanical stress, helping maintain insulating gas pockets even under deformation.

  • Also, under increased hydrostatic pressure (if you dive slightly), properly engineered closed cells resist collapse, preserving insulation.

• Better thermal-to-mechanical balance

  • Because the foam does both insulation and mechanical support, you can optimize the layout of thicker vs thinner zones more precisely. E.g. arms/shoulders can use more stretch foam (with fine microcells) and torso panels can use slightly denser foam to maximize insulation without sacrificing mobility in the limbs.

How does Yamamoto achieve these results with the material?

Making these cells is only possible using old, but incredibly precise industrial equipment handled by skilled artisans at the Yamamoto factory in Japan. It's a testament to their patience and technique that they can control the temperature to within the 0.1 degrees of heat needed to achieve these results. 

The Yamamoto logo symbolizes this perfectly independent cell structure that makes this material light, flexible and warm.  It's their mission to enable people to enjoy the water as comfortably as possible whatever the temperature, and we are proud to have them as partners.