I have contacted Elios asking if they have skin/skin Rubatex for making vintage suits. This is what they replied: Smoothskin Black outside / Open cell inside Neoprene Rubatex G-231 High density. Does this mean skin/skin? Is smoothskin a rubber coating? What does open cell look like and how does it do in keeping warm?
Open cell is a poor choice of words, since it describes man-made sponges. It is really split cells of closed cell Neoprene and looks like the raw end of any closed cell foam Neoprene that has been cut along the edge -- over the entire inside surface. I estimate it has at least 4x more friction when putting on. Soapy water is mandatory. Basically, all those little cells on the surface where the smooth skin has been removed act as tiny suction cups, thus hindering water circulation. Rubatex does not make any open/split cell material, unless it was recently announced.
As mentioned, I have been wearing custom skin-in suits most of my life. Last year I had to get new Scuba suits and tried the new synthetic blended Neoprene that has virtually taken over the market. The design is a 7mm, skin-in, Nylon out, farmer-john, no-zip, pull over beaver tail jacket, with a neck dam. I also recently received a 7mm split-cell custom freediving suit from Oceanos. The design is virtually identical to my other suits except the hood is attached. You will read a lot of posts that say split-cell suits are 2x as warm or that a 5mm split cell is as warm as a 7mm Scuba suit. I think the statements are misleading.
My case is as close to an apples-to-apples evaluation on the effect of split-cells alone as I can imagine. All the materials used in freediving suits tend to be more flexible and stretchy than Nylon-2 Scuba suits. As a result, they are more accommodating of imperfect fits. I contend that a good fit, and the water circulation that it inhibits, is the greatest source of heat retention. This factor is a constant since both suits are custom. In my unscientific estimation, I can’t tell any difference between the warmth of the new split cell suit compared to my Skin-in Scuba suit of the same design. I can move my limbs actively in both suits and can't detect any water circulation, commonly called "pumping".
To be fair, the Freediving suit is probably a little thinner because I need about 4 Lbs less lead than the Scuba suit. Also, most Scuba suits do not hinder water circulation by the suit design as effectively as a 2-piece freediving suit.
Here are some photos that illustrate the design:
MAKO Spearguns - 2-Piece Green Aquatic Open Cell Wetsuit (5.0 mm)
If I were to prioritize factors that make a warm suit it would probably be:
- Fit: Custom if necessary
- Design: Close to a 2-piece freediving suit, which often requires custom
- Skin-in
- Split-cell
As always, your mileage may vary. My conclusions are based on perceptions rather than instrumented engineering analysis.