Newbie questions regarding how wetsuits work

[TSandM]

It isn't even the rubber in the neoprene that keeps you warm -- it's the gas bubbles trapped in it. The useful nature of neoprene is that it traps bubbles in an insoluble and impermeable substrate, so that you can immerse the stuff without the gas being displaced by water. The thicker the neoprene, the more insulating capacity it has.

The ideal wetsuit admits as little water as possible, just enough to fill the air spaces, as described. It then minimizes the exchange of that water with the water in which you are diving, so that you expend only the heat you have to to warm that first bit, and don't continue to lose heat to water that then is lost to the ocean.

A perfect neoprene wetsuit is a neoprene dry suit ( ), but then you do need to add a little air to avoid squeeze. Neoprene dry suits are very warm in shallow water.

 

[nimoh]

It isn't even the rubber in the neoprene that keeps you warm -- it's the gas bubbles trapped in it. The useful nature of neoprene is that it traps bubbles in an insoluble and impermeable substrate, so that you can immerse the stuff without the gas being displaced by water. The thicker the neoprene, the more insulating capacity it has.

The ideal wetsuit admits as little water as possible, just enough to fill the air spaces, as described. It then minimizes the exchange of that water with the water in which you are diving, so that you expend only the heat you have to to warm that first bit, and don't continue to lose heat to water that then is lost to the ocean.

A perfect neoprene wetsuit is a neoprene dry suit ( ), but then you do need to add a little air to avoid squeeze. Neoprene dry suits are very warm in shallow water.

great description

 

[rhwestfall]

Interesting side story - I am actually working with a vendor for a custom WS right now. They are actually suggesting I go to a thinner (5mm vs. 7mm) suite due to the material (stuff mentioned above), because of the insulating capability.....

 

[Lorenzoid]

All the responses so far have been correct - it is the neoprene that keeps you warm, not the water. It is also true that you want to minimize the exchange of body-warmed water with colder, ambient water. A few things so far have not been mentioned:

1. Not all neoprene is created equal. I believe that Thal regularly extols the virtues of Rubatex G-231 neoprene as a suit material. Try searching this string: site:scubaboard.com rubatex neoprene ;
2. Water entering your wetsuit is, in fact, desired. It is a design compromise - you either need to be able to add air to your suit as you descend to offset the growing external pressure of the water (this is called a drysuit) or you need to fill the air-pockets in your suit with an incompressible fluid. A perfectly air-tight wetsuit would continue to compress as you descend, possibly leading to bruising from suit "squeeze." Pouring warm water into a wetsuit before a dive is a good way to get rid of air pockets.

Good explanation. I get it now. So the only reason that water permeability is important is for the pressure equalization aspect, not for any insulating effect. My attempt to sum up my understanding: Neoprene is probably the best material available short of a drysuit because it is semi-permeable or semi-porous but not TOO porous, as a very porous material would not insulate well, and a completely impermeable or non-porous material would need to have the characteristics of a drysuit--that is, the ability to add and vent air. I also suppose neoprene foam might have some sort of cell structure that makes it more suitable than a completely open-cell insulating foam material or completely closed-cell insulating foam material--that is, some mix of closed cells that provide insulation (yet compress with depth) and open cells that let water through.

 

[Crush]

A good description, except that wetsuits are made of neoprene which is impermeable, or effectively impermeable on the timescale relevant for a dive. The water will enter your wetsuit at the wrists, ankles, and neck.

 

[go-scuba-dive]

A good description, except that wetsuits are made of neoprene which is impermeable, or effectively impermeable on the timescale relevant for a dive. The water will enter your wetsuit at the wrists, ankles, and neck.

Yup. It's the water that warms you, which is why it's called a wetsuit. The more layers you add on, the more insulation there is, and as a result the warmer you are. Dry suits are sealed at the neck, arms, and legs not allowing any water to get in.

 

[dfx]

Yup. It's the water that warms you, which is why it's called a wetsuit.

The water isn't warming you, you are warming up the water!

 

[acrofrag]

All the responses so far have been correct - it is the neoprene that keeps you warm, not the water. It is also true that you want to minimize the exchange of body-warmed water with colder, ambient water. A few things so far have not been mentioned:

1. Not all neoprene is created equal. I believe that Thal regularly extols the virtues of Rubatex G-231 neoprene as a suit material. Try searching this string: site:scubaboard.com rubatex neoprene ;
2. Water entering your wetsuit is, in fact, desired. It is a design compromise - you either need to be able to add air to your suit as you descend to offset the growing external pressure of the water (this is called a drysuit) or you need to fill the air-pockets in your suit with an incompressible fluid. A perfectly air-tight wetsuit would continue to compress as you descend, possibly leading to bruising from suit "squeeze." Pouring warm water into a wetsuit before a dive is a good way to get rid of air pockets.

Curious to know the difference between air compressing to the pressure of the water around it vs. water at the same pressure. Why would air cause bruising, but replacing it with a "incompressible fluid" (it is, just not for our purposes here) wouldn't?

 

[dfx]

Curious to know the difference between air compressing to the pressure of the water around it vs. water at the same pressure. Why would air cause bruising, but replacing it with a "incompressible fluid" (it is, just not for our purposes here) wouldn't?

Boyle's law dictates that a gas under double the pressure shrinks to half its volume. An air bubble trapped in your wetsuit thus has half its volume at 10 meters depth than it had at the surface. Since none of the surrounding materials (wetsuit, your body, water) shrink in the same manner (they're all incompressible), that shrinking air bubble can produce a suction cup effect under the right circumstances, for example at a fold in your suit.

 

[Lorenzoid]

A good description, except that wetsuits are made of neoprene which is impermeable, or effectively impermeable on the timescale relevant for a dive. The water will enter your wetsuit at the wrists, ankles, and neck.

Ugh--I thought I understood, but now I'm not so sure again. If neoprene is impermeable to water, then I go back to my original question: Is there not another impermeable material that's a better insulator than neoprene? You could line an impermeable exterior with just about anything.

Also, what about so-called "semi-dry" suits? I thought the whole point of those was that they had seals at the wrists, ankles and neck that inhibited entry of water? That would only make sense if the suit allowed water to enter through some other means--like saturating through the walls of the suit. If a semi-dry suit is effectively sealed, and there is (inevitably?) air trapped inside, then you'd have the same issue as with a dry suit. This is another reason why I was under the (mistaken?) impression that neoprene is semi-porous.