Neoprene compression at depth?

[stuartv]

I have seen numerous posts in here that allude to the way wetsuits compress at depth and, thus, are less warm. This is commonly mentioned in discussing use of Lavacore gear as LC doesn't compress, so it stays just as warm, no matter the depth. And the way it's mentioned generally seems to imply that everyone just takes it for granted that wetsuits are going to compress significantly at depth.

But then I also have seen several posts recommending Wetwear custom suits, so I went and read up on their website. One of the things they tout as their best offering is suits made of NCN (Nitrogen Cell Neoprene). They claim that NCN does not compress (significantly) at depth. That kind of makes me wonder then why don't all suits use that?

So, as best I can figure it, most off-the-rack wetsuits tout some form of super stretchy neoprene, which is supposed to fit better and go on and off easier. Am I correct in thinking that any of those really stretchy suits are NOT going to made of a neoprene that works like NCN? I.e. any super stretchy wetsuit, by virtue of its stretchiness, is also going to be a suit that compresses quite a bit at depth. So, a 5mm stretchy suit at depth might only be 3mm thick.

And, I guess(?), the tradeoff for using NCN is that it's not very stretchy at all. So, if it's not custom made to fit, then there's a good chance it just won't fit right. Either too tight somewhere, or too loose somewhere. And if it doesn't fit well, it won't be as warm as it should be.

Am I correct so far?

If so, then this leads me to think that a Wetwear (or other NCN) 3mm suit would be the warmest 3mm suit I could get - at least, the warmest at depth. Maybe it's the same as stretchy suits at the surface.

So, what depth does the difference start to matter? If I'm only diving to 30 feet, then the stretchy stuff will still be pretty much just as warm as NCN?

What about if I'm diving to 60 feet? At 60', I'm thinking the 3mm stretch will be significantly less warm than 3mm NCN. Yes?

And, at 60' what would be the equivalent to 3mm NCN? Would a 5mm stretch suit at 60' be as warm as a 3mm NCN?

If so, then maybe a good alternative to buying a custom 3mm NCN suit would be to just buy an OTR 5mm stretchy suit? I'm kind of leaning towards an OTR stretch suit for my first wetsuit partly because I'm in the process of losing weight and a stretch suit seems like it would "stay with me" better. And also because I figure resale value on a name brand OTR suit will probably be a lot better than resale of a Wetwear or other custom fit suit if/when I decide to buy a custom suit later.

Last question: Are there any other wetsuits (OTR or custom) that use NCN or similar neoprene?

 

[tbone1004]

ok, so some basic physics
Neoprene is a closed cell foam, meaning that as pressure increases there is no way to equalize, so the volume becomes smaller. At 33FSW, there is 2ata of pressure on the suit so it is 1/2 as thick, with 1/2 the volume of air for insulation. This air volume can be slightly manipulated by making the foam more dense so it will resist the pressure differential marginally, or the foam can be manufactured under pressure which is I think how the Nitrogen Charged Foam is made. They make it under pressure so when it comes out, there is residual pressure inside of the foam, so the pressure equalizes at some sort of depth instead of at the surface.

Lavacore isn't actually neoprene, but is basically some Polartec with some GoreTex *Lavacore uses a Polyurethane film, so it's not nearly as effective as the teflon base Gore uses, but same idea of semipermeable membrane* and then whatever the outer surface is. It works by trapping the water and not allowing it to move, so with no air spaces in the suit, it is essentially neutrally buoyant as well as depth compensating.

A 5mm suit becomes 2.5mm at 33 feet, and 1.7mm at 66 feet. The not quite so stretchy neoprenes may end up being 3mm, and 2mm, but it's not anything really significant. They also lose buoyancy, and that was the original reason behind developing a buoyancy compensation device, to compensate for the change of wetsuit buoyancy at depth.

You don't mention your diving environments so it's hard to offer advice. If you are regularly diving in very cold water and very deep, you need a drysuit, that's just the way it is, especially if the air is as cold as the water. If you are doing mostly shallow stuff, <40ft, then you can just get a wetsuit that is one step warmer than you would normally get so you stay warm at depth. You'll be a little warm at the top, but you'll survive. If you're in 5mm territory, which for me is anything warmer than about 55F for a full day of relatively shallow diving, then you may as well stay with a cheaper stretchy suit, they're more comfortable anyway. Neosports are decent suits for the money, not quite as durable as the waterproofs or some of the other high end stuff, but they work well. Pinnacle has the merino line suits which actually hold quite a bit of head, though if you're doing lots of diving on that, I recommend fitting a P-valve to it so you aren't contaminating the suit. Wool is naturally antibacterial, but it only works so well

 

[stuartv]

ok, so some basic physics
Neoprene is a closed cell foam, meaning that as pressure increases there is no way to equalize, so the volume becomes smaller. At 33FSW, there is 2ata of pressure on the suit so it is 1/2 as thick, with 1/2 the volume of air for insulation. This air volume can be slightly manipulated by making the foam more dense so it will resist the pressure differential marginally, or the foam can be manufactured under pressure which is I think how the Nitrogen Charged Foam is made. They make it under pressure so when it comes out, there is residual pressure inside of the foam, so the pressure equalizes at some sort of depth instead of at the surface.

I should have posted this link before. It has a video showing how the various neoprenes compress under pressure:

Wetwear - Hyperbaric Chamber Test Wet Suits for Neoprenes - How does yours hold up? (skip ahead to the 1:00 or so mark to get to the good stuff)

The NCN compresses some at 1 ATM, and then doesn't compress any further all the way down to 4 ATM. The "regular" neoprenes all compress quite a bit more than the NCN at 1 ATM, and then compress more as each ATM of pressure is added. At 4 ATM, the NCN still has most of its original thickness. And the "regular" 3mm neoprene is more like 1mm. And the 5mm is less than 3mm.

IOW, it looks like the regular neoprene behaves as your "basic physics" would predict. But, the NCN does not. That's why I'm wondering what the downsides are to the NCN, so I can decide whether to order a Wetwear custom suit or just stick to a cheaper suit for now.

If I need to buy a 5mm "regular" suit just to be warm at 60' and I could wear a 3mm NCN suit and be just as warm or warmer (at 60'), then maybe I should just go ahead and ante up for the good suit. OTOH, if the downside to the NCN is that it's not nearly as stretchy, so it's more of a PITA to put on/take off, and if I'll have to have it altered if I lose 10 or 20 pounds, then maybe I should just buy the cheaper suit for now.

If anyone has an firsthand experience with what (if any) the downsides are to an NCN (e.g. Rubatex 231) suit, I'd love to hear about it.

---------- Post added September 18th, 2014 at 02:59 PM ----------

ps. Re: diving environments. I'm planning for reefs and cenotes in Riviera Maya, Mexico, in December, and then Oahu, Hawaii, in March.

 

[tbone1004]

for that diving you really aren't going to be able to justify that high end of a suit. I didn't realize that that was the same as rubatex. Basically they have more neoprene, less air bubbles in there, hence the lack of compression. More air=more compression=more flex and vice versa. All suits stabilize at some sort of depth, and that depth depends on how much air is in the rubber vs. actual rubber.
The Deco Stop
read that thread before you buy. In those temps though you may as well just buy a cheap suit until your body stops changing. I have a rubatex hood and I hate it because it is so stiff. It's warmer than all get out, but still really hard to move in.

For that type of diving, just buy a neosport, tilos, or whatever you can get cheap in your size and dive it. The water temps are nowhere near cold enough for you to notice a huge difference in insulation quality at this point.

 

[BRT]

And more air = more insulation

 

[stuartv]

Thanks, guys.

tbone, I read that whole thread. Those guys did not have ANYthing good to say about Wetwear customer service. OTOH, I did note that the thread was from 2004. What I have read on here about Wetwear has been almost all very positive about their suits and their customer service. Maybe they've improved from 10 years ago?

Anyway, point well taken on expensive custom vs less-expensive OTR. I do believe that's what I'll go for.

And, BRT, thanks for making that point. It hadn't occurred to me that the same thickness of stretch neoprene might actually be warmer than NCN.

 

[tbone1004]

it's a fine balance though and that's where everything gets skewed. While the higher air volume might keep you warmer at the surface, the higher rubber concentration resulting more of the thickness staying where it should be keeps you more consistently warm at depth. It's a delicate balance. If you want to stay as warm at 150ft as you are at 50ft and you are adamant about staying in a wetsuit, then yes the rubatex and NCN stuff is better, that's why a lot of us have hoods made out of that material. The hood is the most critical part of any exposure protection and can be the real difference in feeling cold but surviving, and going hypothermic. On the other hand, in relatively warm water at relatively shallow depths, it's a tossup.

 

[dfx]

A 5mm suit becomes 2.5mm at 33 feet, and 1.7mm at 66 feet.

Just nitpicking but this isn't actually true. Gas compresses at depth as you describe, but neoprene isn't only made out of gas. Its other component, rubber (or whatever other solid you use), doesn't compress as pressure increases and so the actual loss of thickness depends on how much gas is trapped in the neoprene. Of course, since the primary ingredient in providing thermal insulation is the gas, loss of this insulation due to compression still applies.

 

[stuartv]

it's a fine balance though and that's where everything gets skewed. While the higher air volume might keep you warmer at the surface, the higher rubber concentration resulting more of the thickness staying where it should be keeps you more consistently warm at depth. It's a delicate balance. If you want to stay as warm at 150ft as you are at 50ft and you are adamant about staying in a wetsuit, then yes the rubatex and NCN stuff is better, that's why a lot of us have hoods made out of that material. The hood is the most critical part of any exposure protection and can be the real difference in feeling cold but surviving, and going hypothermic. On the other hand, in relatively warm water at relatively shallow depths, it's a tossup.

Right. That balance is what I was getting after reading and pondering on BRT's post.

And, as I am just getting my OW certification, I reckon I really don't need the NCN at this point.

 

[tbone1004]

Just nitpicking but this isn't actually true. Gas compresses at depth as you describe, but neoprene isn't only made out of gas. Its other component, rubber (or whatever other solid you use), doesn't compress as pressure increases and so the actual loss of thickness depends on how much gas is trapped in the neoprene. Of course, since the primary ingredient in providing thermal insulation is the gas, loss of this insulation due to compression still applies.

that is true, but the insulation qualities are about equivalent to those numbers. The loss factor stops when it equalizes, and it's not truly linear. Probably closer to 3mm and 2mm then stabilizers shortly thereafter