Northwest Dive Club

Come all ye physics geeks. I would like to resolve this issue for good. In so many places, including a current instructor's manual I read this type of statement "With a wet suit, a thin layer of water between the diver’s body and the suit serves as insulation." Other say no way, "water always draws body heat away from your body and is not an INSULATOR."

A course director argues that when the water in a wetsuit warms to body temperature, it then is an INSULATOR.

What say you??? Please include the science to support either side.

If the water was an insulator we would all dive our drysuits flooded.

Ha Ha

The wetsuit is the insulator, not the trapped water.

Actually, water is a pretty good heat conductor.

Magoi wrote:Actually, water is a pretty good heat conductor.

And that is why we use it in radiators....to get rid of heat.

Water is not an insulator. Insulators have a low specific heat and poor heat transmission -- water has a high specific heat and excellent heat transmission.

The insulation in wetsuits is the nitrogen bubbles in the rubber. Water is tolerated because it is more expensive and difficult to make a suit that seals (as any dry suit owner knows). Excellent wetsuits are close-fitting and have little water exchange, so the water that enters is warmed to body temperature (with a concomitant loss of body heat) but then remains in place, so you are not constantly heating new water.

I've dove wet and dry for three years...drysuits suck imo. Expensive, fragile, and result in a lot of cancelled dives.

Jeremy wrote:I've dove wet and dry for three years...drysuits suck imo. Expensive, fragile, and result in a lot of cancelled dives.

Yeah but they insulate

That "thin" layer of water inside a wetsuit is not an insulator. Never has been, never will be despite all marketing hype to the contrary. LCF explained why.

Thanks for all the comments.

However, I am debating the issue with someone who is creating curriculum for certifying divers and currently believes that water inside the suite after being warmed to body temp becomes and insulator. I really need some hard science that will convince the other side to change his view.

You've already heard from a practicing physician ......

Your friend does not understand what insulation is.

Every calorie of heat given up from the skin to a molecule of water in that thin layer of water inside a wetsuit is (for all practical purposes) immediately available to be transfered to the wetsuit rubber itself. That's not insulation, that's conduction. Insulators by definition prevent or limit conduction, convection or radiation. Those are the 3 ways heat energy can move from one thing to another. Water actually facilitates conduction - most liquids do, water's actually one of the best conductors there is. BTW The water in the suit does nothing to limit convention or radiation either.

This is why tighter wetsuits and semidry suits are warmer. The thinner that layer of water the better and no water at all would be warmest. Glueing the neoprene directly to your skin I suppose.

Has anyone every said? "Goretex schmortex, that thin layer of sweat inside your shell outwear is an insulator. As you sit on the top of Mount Rainier it's insulating you." Of course not.

CaptnJack wrote:Your friend does not understand what insulation is.

Every calorie of heat given up from the skin to a molecule of water in that thin layer of water inside a wetsuit is (for all practical purposes) immediately available to be transfered to the wetsuit rubber itself. That's not insulation, that's conduction. Insulators by definition prevent or limit conduction, convection or radiation. Those are the 3 ways heat energy can move from one thing to another. Water actually facilitates conduction - most liquids do, water's actually one of the best conductors there is. BTW The water in the suit does nothing to limit convention or radiation either.

This is why tighter wetsuits and semidry suits are warmer. The thinner that layer of water the better and no water at all would be warmest. Glueing the neoprene directly to your skin I suppose.

Has anyone every said? "Goretex schmortex, that thin layer of sweat inside your shell outwear is an insulator. As you sit on the top of Mount Rainier it's insulating you." Of course not.

Well said!

JasonDiver wrote:However, I am debating the issue with someone who is creating curriculum for certifying divers and currently believes that water inside the suite after being warmed to body temp becomes and insulator. I really need some hard science that will convince the other side to change his view.

LCF and CaptJack said it all. Water isn't an insulator, but if the warmed water stays put at least you don't lose any more heat.

If that isn't enough, I guess someone can find a physics textbook or engineer's handbook of materials properties.

Actually, here is a PDF of some kind of classroom lesson on thermal insulators:
http://genesismission.jpl.nasa.gov/educ ... op_4ST.pdf

It includes a table listing the coefficients for a variety of materials including water and air.

Matt S. wrote:
LCF and CaptJack said it all. Water isn't an insulator, but if the warmed water stays put at least you don't lose any more heat.

If that isn't enough, I guess someone can find a physics textbook or engineer's handbook of materials properties.

Actually, here is a PDF of some kind of classroom lesson on thermal insulators:
http://genesismission.jpl.nasa.gov/educ ... op_4ST.pdf

It includes a table listing the coefficients for a variety of materials including water and air.

I thought that was it, but the link from jpl says "Water and wood are insulators, and are not good conductors of heat" so that sounds confusing.

JasonDiver wrote: I thought that was it, but the link from jpl says "Water and wood are insulators, and are not good conductors of heat" so that sounds confusing.

Its all relative. Look at the table on page 2 again: water has 2x the conductivity of skin and 20x the conductivity of air. So having a layer of air in your wetsuit would be more insulating, ditto having an extra layer of skin.

Sure - relative to copper or aluminum water could be considered an "insulator". However you aren't subsituting those materials for water in a wetsuit. The water is displacing air and any water inside is not insulating you. If water were an insulator, then being naked in Puget Sound would be gloriously balmy.

Thanks for the help. I will take the case back to this course director. I will let you know if we made a difference.

JasonDiver wrote: However, I am debating the issue with someone who is creating curriculum for certifying divers...

Oh really! We've had some interesting posts about certain people who tried to DIY their own dive agency. Anybody want to dig through the archives?

renoun wrote: Oh really! We've had some interesting posts about certain people who tried to DIY their own dive agency. Anybody want to dig through the archives?

No. This is for one of the major dive cert agencies.

For someone to get as far as a course director and believe that water is an insulator inside a wetsuit is a scary thought. They would have to willfully disregard an overwhelming body of evidence to the contrary, including published material from PADI, SSI and others.

GearHead wrote:For someone to get as far as a course director and believe that water is an insulator inside a wetsuit is a scary thought. They would have to willfully disregard an overwhelming body of evidence to the contrary, including published material from PADI, SSI and others.

Well it is compared to your old skool lead lined wetsuits... Ahh those were the days with real intergrated lead.

That a course director would have this wrong sadly does not surprise me. Most people headed into the professional levels in scuba find the physics exam to be the hardest part.

This quote, "With a wet suit, a thin layer of water between the diver’s body and the suit serves as insulation." is copied from a current edition of an OW instructor's manual.

JasonDiver wrote:This quote, "With a wet suit, a thin layer of water between the diver’s body and the suit serves as insulation." is copied from a current edition of an OW instructor's manual.

I've read that for years and it is nonsense. However it actually does serve as insulation because it has some resistance to heat transfer. Even aluminum has some resistance to heat transfer so with enough inches of aluminum and enough heat to heat it up you would eventually reach equilibrium. With water in a wet suit the water keeps exchanging so you won't ever reach that point. That and the fact that waters insulation value is 1/24th that of the nitrogen in the neoprene makes the statement ludicrous. http://www.engineeringtoolbox.com/therm ... d_429.html

There are a lot of things taught as facts that are not true. But a lot of people accept whatever they read in a book or hear from an "authority" without thinking about it. And sometimes you have to either accept a lower grade on the test or just tell the teacher what they want to hear.

Brian

JasonDiver wrote:This quote, "With a wet suit, a thin layer of water between the diver’s body and the suit serves as insulation." is copied from a current edition of an OW instructor's manual.

Yup very common phrase and completely erroneous. Of the 3 materials in the system, skin, water, neoprene rubber (the solid) and the nitrogen bubbles in the neoprene, water is by far the least "insulating".

Boiling water in a pot (212F) would "insulate" you from the 1200F flames of your gas stove however, so its all relative.