Understanding differences between undergarment materials

I recently bought a shell suit and used a thick fleece jumpsuit for my dives in it so far. I have been looking at different undergarments to see what the options are. It seems one of the things to consider is what is used for insulation. I'm sure an undergarment decision is just as personal as other equipment choices, so there is no right or wrong....but....I would like to make sure my understanding of the properties of the different materials is correct. Please help correct inaccuracies below and I can update this post with the info. I know that for any undergarment you need a base wicking layer, but here I am focusing on the insulating layer.

Fleece: One of the least expensive options for insulation. It is bulky to pack and doesn't compress as much as other types of insulation, which means when you dump air from the suit you will be more positive buoyant than with other types of insulation. Fleece is less affected/enhanced by adding air to the suit; adding air is more just for relieving squeeze. In terms of the amount of warmth you get for a given amount of bulk, fleece doesn't insulate as well as other materials. Fleece also acts as a wicking layer.

Thinsulate: An older synthetic insulation that is kind of a middle tier insulator in the outdoor gear world, but seems to hold higher rankings in the dry suit undergarment world. When compared to other synthetic fiber insulators, Thinsulate is stiffer, heavier and doesn't compact as much. For backpacking that is bad, but for a dry suit the lack of compaction can be a good thing in that when you dump air from the suit the Thinsulate will have more warmth than the newer lighter loft synthetic insulations out there today. For a given thickness, Thinsulate is a better insulator than fleece and is more affected by the air volume in the suit than fleece is. Less compaction also means more positive buoyancy after dumping all air from the suit (i.e. you'll need more weight to hold a safety stop if your style is to dump most or all air from the suit at that point). Synthetic fiber insulators need a separate wicking layer. If you are trying to get maximum warmth with minumum air in the suit, then Thinsulate seems to be the best choice, but at the cost of more restricted movement than with the light loft insulators. Fleece comes second for that.

Primaloft and other "light loft" insulators: A modern and top tier insulator in the outdoor gear world. It is lighter and more compactable than Thinsulate and fleece. It retains more warmth when wet than the others do. Higher compaction means less bulk/positive buoyancy when air is dumped from the suit, and it also means the insulation quality/level is more affected by air volume in the suit. This can be seen as good in that you have a wider thermal range for the insulation - if you get warm, dump some air from the suit and the resulting compaction drops the insulation level of the material. This can be bad if you feel like the Michelin Man in order to get warm. For a given thickness, these light loft insulators give more warmth than others on land, but because they are more affected by air in the suit, that might not be the same for a diver who just adds enough air to make the squeeze not so uncomfortable. I have heard that the light loft of the insulator combined with a thin nylon outer shell can get in the way of the exhaust valve in the dry suit, like it can get sucked up against the valve and slow down or prevent air from getting out of the suit.

Polartec Power Stretch: A woven, wick-able, stretchy material that can be used as a heavy base layer or as a primary insulator for less cold environments. Probably similar in warmth to 100g fleece but more stretchy than fleece?

Cotton: Forget it. It doesn't insulate when wet and doesn't dry fast.

It would be great to hear from people who have different types of undergarments - how they work and how they affect the amount of weight the diver needs for the same dry suit.

I am leaning towards a light loft insulator since my fleece feels so bulky. I think that bulkiness requires me to carry more lead just to get down and stay down for a safety stop. I do wonder of the "air in the suit" requirements of the light loft insulators will defeat lead shedding...will it be like "OK I have enough to get down, but I don't have enough to stay warm?"

Each material has advantages and disadvantages.

Depending on temp, I use various combinations of Polartec fleece, polypropylene and Weezle wear.

Polartec is quite compressible and I find that more layers are required to get adequate loft and warmth. Like polypropylene, Polartec is able to stretch and feels soft, so it's very comfortable. Both breathe very well, so the skin will stay drier and warmer. Launders easily. Dries quickly. Loses most of its insulating value when wet.

Weezle is quite compressible, and has a shell, so it needs to fit well to allow full range of motion. It traps air better than Polartec and is warmer as a result. Laundering requires more care. Retains quite a bit of insulating value when wet.

I haven't tried Thinsulate or Primaloft, but they both appear to require a shell and therefore would not be able to stretch. Good fit would be important.

Thinsulate would probably require less loft, since it traps air in microfibers. I've felt the material and I think it has less bulk, less loft, and would require less lead weight than fleece. Pretty efficient insulation for a given thickness or weight. Laundering is more difficult. Dries more slowly I've heard. I wonder if it tends to get clammy easier. On the other hand, it retains much of its insulating value when wet.

I'm going to try it sometime since it's less compressible and more compact, but I'll be careful to get a good fit. I'm thinking it will be warmer in dorsal areas of my body which tend to get a little cold in the winter when my present materials compress.

I don't know about Primaloft, but it's touted as a synthetic down-like material. Might be similar to Weezle. I wonder how it works when compressed.

As far as the amount of weight each material might require, I don't worry about it....I'm just concerned with being nice and warm.

That's my two cents.

Dave C

I bought my 3 layer quilted undergarments off ebay from rondel....its has a fleece layer, a thinsulate type layer and a nylon layer. It combines the best of all the worlds.....It is warm into the upper 40's....If going cooler than that I wear a nice set of thermal underwear and a lycra to help get into/out of the 3 layer suit.....I believe this winter I will be wearing a set of 100g fleece under my lycra...and then the 3 layer undergarments.....I have under $100 into the components.

hollywood703:

I bought my 3 layer quilted undergarments off ebay from rondel....its has a fleece layer, a thinsulate type layer and a nylon layer. It combines the best of all the worlds.....It is warm into the upper 40's....If going cooler than that I wear a nice set of thermal underwear and a lycra to help get into/out of the 3 layer suit.....I believe this winter I will be wearing a set of 100g fleece under my lycra...and then the 3 layer undergarments.....I have under $100 into the components.

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I've been looking at that undergarment, since everyone seems very happy with it here.

I'm curious, do you know if it uses Thinsulate "B", the hydrophobic type?

Do you think it gets clammy at all, such as on repeat dives or sweaty, heavy exertion dives?

Dave C

Thought these may be of interest to this thread... The first is an older NEDU report but one of the few documents available. The second is a recent review by Bob Stenton at DUI presented at a Smithsonian/ AAUS Advanced Scientific Diving Workshop.

Insulation, Compressibility and Absorbency of Dry Suit Undergarments.
Sterba, Hanson, and Stiglich. 1989
RRR ID: 4867

Stinton RT. Survey of Thermal Protection Strategies. In: Lang, MA and Smith, NE (eds.). Proceedings of Advanced Scientific Diving Workshop: February 23-24, 2006, Smithsonian Institution, Washington, DC.
RRR ID: 4658

If these were of interest, more on thermal protection can be found in our "Suggested Reading List".

Gene_Hobbs:

Thought these may be of interest to this thread... The first is an older NEDU report but one of the few documents available. The second is a recent review by Bob Stenton at DUI presented at a Smithsonian/ AAUS Advanced Scientific Diving Workshop.

Insulation, Compressibility and Absorbency of Dry Suit Undergarments.
Sterba, Hanson, and Stiglich. 1989
RRR ID: 4867

Stinton RT. Survey of Thermal Protection Strategies. In: Lang, MA and Smith, NE (eds.). Proceedings of Advanced Scientific Diving Workshop: February 23-24, 2006, Smithsonian Institution, Washington, DC.
RRR ID: 4658

If these were of interest, more on thermal protection can be found in our "Suggested Reading List.

Click to expand...

Very interesting and well worth the quick registration to read the second study! Thanks for posting.

The first study really nails down the superiority of Flectalon and Thinsulate.

I'll have to check out Northern Diver's Metalux and Flectalon undersuits (half-way down the page):

http://www.diveutc.com/NorthernDiver.html

Thanks again.

Dave C

Good info here, I just switched to a shell suit and suddenly I need new undergarments.

I wanted to chime in that wool kicks *** as an undergarment material - I use a wool army sweater and its absolutely brilliant. Now if only I could find woolen long johns I would be one happy camper

dave......It is a thinsulate type material...a knock off....I always wear a wicking material under my suit to soak up the sweat and change out that in between if needed. (I use a T-shirt most of the time) I have not used any brand name undergarments...but with the quality i see and for the price, I wont waste my money.

Gene - great info, thanks for posting that. So those studies show that:
- For a given thickness, Thinsulate performs a little better than twice as good as fleece.
- When wet, Thinsulate performs better than fleece
- Fleece is slightly more compactable than Thinsulate

The first study seems to also show that a high loft material (with high compressibility) performs well in terms of thermal insulation, but it doesn't measure the insulation value when compressed....only when wet.