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How much warmer is 7mm than 5mm?

JamieC

Member
Oct 9, 2020
5
3
8
27
Lake District NW England
I currently have a 5mm open cell wetsuit, it's a budget suit that I bought a little over a year ago and was/is my first suit. I struggled through last winter in it but I'd like to get something warmer for this winter. I dived this weekend in it in 6 degree water and was freezing after about 2.5 hours. Water temps around here drop down to around 5 degrees over winter.

I also think that I may be on the upper size limit of my current jacket so a new one wouldn't be such a bad thing, also means I've no chance of getting a vest on underneath.

I was thinking of buying a 7mm jacket to begin with and see how I get on, and if needed I could then get some 7mm pants. But the price of 7mm jackets isn't far off some heavily discounted full 7mm suits, so I may as well buy a full suit and potentially save money in the long run/end up with a better quality suit (full suits seem to be more heavily discounted than individual jackets/pants).

But then I wonder; how much warmer is 7mm than 5mm? Is that 2mm actually going to make that much difference? I've also seen some 9mm suits?
 

JamieC

Member
Oct 9, 2020
5
3
8
27
Lake District NW England
Wow 6 degree water sounds like you need a dry suit. Where are you located where the water is so cold. Never mind I looked at your profile. England waters are cold is it like that all year round?
Hi, well I'm no expert on sea temperatures, and I swim in the lakes and old flooded quarries, but I know it's never very warm :LOL: I live in the north of England, but whenever I've swam/dived in the sea off the south coast it has been noticeably warmer than the lakes up here. There are some very committed wild swimmers up here, who will swim considerable distances in the lakes and tarns in just trunks or bikinis all year round, even cracking the ice to get in sometimes!
 
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Bill McIntyre

San Clemente, CA
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There are lots of variables to consider. It I’ll start by saying that a 7 mm suit is significantly warmer than a 5 mm suit IF they are exactly the same quality and fit. But if your 5 mm isn’t a perfect fit or the same quality rubber then maybe a better 5 mm suit is all you need. Maybe you really need a custom suit?

But then I have no experience with such cold water.
 
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JamieC

Member
Oct 9, 2020
5
3
8
27
Lake District NW England
There are lots of variables to consider. It I’ll start by saying that a 7 mm suit is significantly warmer than a 5 mm suit IF they are exactly the same quality and fit. But if your 5 mm isn’t a perfect fit or the same quality rubber then maybe a better 5 mm suit is all you need. Maybe you really need a custom suit?

But then I have no experience with such cold water.
That had crossed my mind, I'd been wondering if it was more the quality of my current suit rather than the thickness. But if I was to buy another suit, I'd rather have a good quality 7mm than another 5mm, it's only going to get colder here and it gives me more options.

I'd also rather stay away from custom for now, until I've a bit more experience and feel I deserve one
 
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Bill McIntyre

San Clemente, CA
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I just did the conversion, and the sea temp in Southern California gets down to about 11C. Thats definitely 7 mm territory for me and most of my friends.

But I'm not so sure about "deserving" a custom. For decades I struggled with off the rack suits and they never fit. I have a huge head, a long torso, and short legs. For the last 25 years of so I've used custom suits and the difference is dramatic. If you need custom, you need custom. We don't get points for suffering.
 

Kodama

Well-Known Member
Jun 20, 2016
400
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Belgium - California
www.eastwind.be
I personally have very little ‘natural neoprene’ and appreciate a warm suit for the cold murky waters i dive. My experience tells me that a custom 5mm can almost be as warm as a ‘not quite perfect fitting’ off the shelf suit.

In winter with water that gets very cold to 10 degrees C, i use a 8mm suit with sheico neoprene because it does not compress too much at depth so it keeps me warmer during the dive.
In contrast Yamamoto neoprene is softer and probably a bit more insulating at the surface but it compresses much more at depth making you feel colder during the dive.

Basically i switch between 5 and 7/8mm depending on season.
In General you could say that a custom suit will be performing better then of the shelf suits unless they fit you perfectly. There is a big difference between a perfect fit and a not so perfect fit in terms of insulating performance.

If you are in six degrees of water I would recommend a 8mm suit. Maybe even with a 2mm undersuit tank top. When the water is that cold i get out in the kayak every 40 minutes to drink hot tea and warm up from the inside out.
A perfect fit is even more critical here to make sure the suit stays virtually dry since thermal conductivity of water is so much larger.

A pee valve is a great thing to have too. I used to laugh with my buddies who sported one but not anymore. You can pee as much as you want without any water entering the suit keeping you warm sooooo much longer. And then there Is the added benefit of hygiene and complete lack of odor. I never go back no matter how much fun my friends make of me!

Fyi being in the water 5 to 6 hours is common for me, in the winter that is reduced to 2to 3 hours.
 
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Mr. X

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I have an old 5mm made-to-measure Elios basic Ecoline spearo suit and a newer 5.5mm off-the-shelf Mares, I think the Elios is a little warmer, despite its age. The Ecoline neoprene is stiffer and retains its loft better, as the suit fits very well, it doesn't need to stretch much.

The Elios made-to-measure suits was one of the best purchases I ever made. A good investment.

Both are good suits though and both excellent value when I purchased them. The Elios because the pound was strong, the Mares because it was on sale. Made-to-measure is well worth it, if you are not a standard size/shape. They should make it easier/cheaper to mix and match tops and pants of different sizes.
 
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Bill McIntyre

San Clemente, CA
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For over 20 years I have been getting custom suits made by a local firm in Southern California. They don't use the latest soft stretchy neoprene, but I liked the fact that I could drive an hour to their shop, let them do the measurements, and then drive back to try it on rather than have them ship it to me. In a couple of cases when I tried it on it wasn't quite perfect, and they told me to go to lunch while they adjusted it. But recently a lot of people have been raving about custom Polosub suits offered by a local shop. The shop does the measurements and sends them to Italy, and in a month or so the suit comes back. I was really worried about how it would be handled if the suit didn't fit. Would we send it back to Italy? Who would pay for that? Luckily, I didn't find out. The suit is probably the best fitting most comfortable suit I've ever owned.

So this is one vote for Polosub. Your results may vary.

Edit- that Polosub cost $420 US delivered.
 
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p33

Member
May 12, 2017
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If you can get along with a 5mm normal-ish suit in 6C water for about 2.5 hours, I can only take my hat off... Concerning the suite: I'm spearfishing in Spain and here the water here gets down to about 11-12C both in the Atlantic and the Mediterranean. The most usual combination for those lowest temperatures here is 7/5, meaning jacket - 7, pants - 5. Most of the spearos here use the bare neoprene suits (no nylon or whatever lining on both sides), and it *does* make a hell of a difference. If you can go good brands, as somebody suggested already, go Polosub, Elite, Marea or whatever brand that make *only* wetsuites. They'd offer you different kinds of neoprene: Yamamoto, NJN, Daiwa. Yamamoto is the softest and the warmest (but compresses more as you go down), Daiwa is a "cardboard" (IMHO!), NJN seems to be the happy medium (IMHO!) - if you dive reasonably deep withe constant weight, it is possibly the best choice. All good brands would offer you to fill in a form with your sizes: do it! Send it to them and ask whether you fit in their standard size. If they say yes - good for you, if they suggest to make some custom adjustments - it wouldn't hurt too much (Elite offered me those for about 30 euros, just to make an example). I suppose you already have a valve for peeing put onto your pants, don't you?..
 
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