About Wet Suit Material

Wetsuits are typically made from material that is either 100% Neoprene, or a blend of Neoprene and Butyl rubber. The sponge is the middle layer, and the surface can be either skin (smooth “waterproof”-textured rubber), coated (like the slick finish of Henderson’s Gold suits), or laminated with fabric (nylon, polyester, and Kevlar are examples).

Closed Cell Sponge Rubber

In the Elastomeric Industry (the companies that manufacture rubber for all its various uses), the technically correct term for closed cell sponge rubber is expanded rubber. The cells are like individual balloons, holding gas and not allowing moisture to pass through as long as the cell wall has not burst. The chemical compound for sponge may be the same as for solid rubber (like O rings and gaskets).   To create the sponge cells, the raw compound is mixed with a “chemical blowing agent”. Under the heat and pressure of the forming process, this additive decomposes and mixes with the rubber compound and generates nitrogen or CO2 gas (depending on the compound used). As this reaction is occurring, the mixed batch is placed into an oven and allowed to expand into a bun from 2″ to 4″ thick. The bun of closed cell sponge rubber is then aged and sliced into sheets. These sheets are the basis of ALL modern neoprene wetsuits.

So what is open cell sponge rubber? In the Elastomeric Industry, it is expanded rubber that is designed specifically to be lightweight and rebound completely after compression. This type of sponge rubber is typically used for sound deadening or absorption, not wetsuits.

Some wetsuit companies use the term “closed cell” to refer only to sponge that has been cured to have the smooth skin on both the inside and outside. Such suits are used primarily by competitive swimmers and free divers, because it is believed the texture is more hydrodynamic. The term has been further misused by some wetsuit companies to differentiate their product from their competitors; along with the claim that their closed cell neoprene is non-porous’ (implying porous neoprene is bad).  Let me say this about that… HORSE-FEATHERS!!

Porosity is the space between the cell walls that makes the structure of the sponge.  If there was no porosity, there would be nothing but solid rubber, which would be a whole different material (O rings and latex).  Permeability is the connection of pore spaces from one side to the other, which allows water to seep through the material.  Permeability is created by constant deflection of closed cell sponge rubber.  Bending, over-compression, or over-stretching of the closed cell sponge may cause the cell walls to burst. When a closed cell sponge has been over-compressed, the sponge may rebound very slowly, or not at all, compromising the integrity and insulating ability of the material. The degree to which the material will rebound after deflection and the percent to which the material will stretch without tearing the cell walls are properties which can be controlled at the time of manufacturing the sponge rubber.  These properties are discussed in ASTM D1056, ASTM D6576 and Mil-R-6130C. Companies that manufacture neoprene sponge rubber to be used in wetsuits offer different grades, reflecting differences in these properties, and hence differences in application.  The inside sponge and the outside surfaces all contribute to the attributes of the wetsuit material, and hence the attributes of the final wetsuit.

Which type of sponge is best? Generally, 100% Neoprene rubber has a greater capacity to withstand compression (maintains thickness under greater pressure), and is more likely to rebound to original thickness after repeated or severe compression than the Neoprene-Butyl blend rubber.  However, blended rubber generally has greater capacity to stretch and flex without tearing the cells walls than 100% Neoprene. Terrapin offers both Glomex Neoprene-Butyl blend rubber and Yamamoto calcium carbonate – based neoprene (made from limestone). Yamamoto says their rubber has a 23% higher close cell structure than petroleum- derived neoprene, making it more buoyant, while also having a maximum elongation of over 480%, where human skin stretches only up to about 60- 70%.

What’s trendy? Hyperstretch is a trade-marked name for a very stretchy, high-butyl-content rubber sponge.  It is typically laminated with a relatively open-knit fabric, which can stretch as much as the underlying sponge without delaminating.    Insta-Dry is a 3-stack laminate: skin outer surface on sponge/laminated to nylon/laminated to sponge with a slick-coated inner surface.  The nylon fabric in the center gives a layer that the stitching can hold into.

Surface Finishes

Skin: The sponge can be cured (a.k.a. melted) again after slicing to get a smooth surface where all the bubbles are sealed.  This makes an excellent surface seal against the body (like the neck and wrist seals on dry suits). But skin finish is not resistant to abrasion and it can’t hold a stitch, only glue, so it is more vulnerable to tearing.  Why is it popular today? This was the first finish available on the first wetsuits (remember Cousteau, Bond, and Nelson?), and retro is cool.  Also, not coating or laminating fabric on the sponge saves $, so the wetsuit can be made more economically.

Coated: New technologies have produced coatings that can be sprayed onto the sliced sponge.  These include the SCS Metal finish produced by Yamamoto Rubber and Glomex Rubber’s equivalent (marketed under various names like Henderson’s Gold finish, and Harvey’s Cobalt, etc…).  This finish has a powdery slick feel when dry, allowing the material to slide easily over the body, and is hydrophilic (sticks to wet surfaces) when wet, reducing the ability of water to flow between it and the body.  Because the smooth texture doesn’t hold water it dries faster than neoprene with a fabric surface.  And it doesn’t trap the body’s skin cells like fabric can, so it is somewhat antimicrobial.  But it also can be vulnerable to tearing and can (will) wear off with repeated rubbing.  Some organic chemicals cause it to wear off faster (so it’s best to avoid sunscreens and perfumes).  Manufacturing processes have improved since these coatings first hit the retail market, so the finish now lasts longer, but it can still wear off eventually.

Fabric: Laminating fabric to the sliced sides of the sponge provides strength (resistance to tearing and abrasion), style (colors and patterns abound), and the ability to slide over the body (compared to skin surface).  Where wetsuits are stitched together, it is the fabric that actually holds the stitches in place.  Special fabrics can be used to amplify specific attributes, for example: Kevlar, Kanoko, and Cordura are very abrasion resistant, Lycra nylon slides easily, and fleece holds water in place, providing better insulation so it feels warmer.  Titanium can be added to the laminating glue, which some manufacturers claim will reflect body heat back to the wearer.  Since metal actually conducts energy (heat, etc.) better that rubber or nitrogen, a strong argument can be made against the “reflection” theory.  The greatest benefit from Titanium might be that it strengthens the laminating glue and may plug up the permeability of thinly sliced neoprene, such as 2 mm or thinner.

Polartec & Dive Skins

Polartec is an engineered material, composed of three layers:  Lycra nylon on the outside, nylon fleece on the inside, with a layer of polyurethane sandwiched in-between.  Polartec is a Malden Mills trade name.  An equivalent product made in China is called Lavacore.  This material contains no sponge rubber, so it is neutrally buoyant, and can be worn by many people who are allergic to Neoprene.  It is about 2 mm thick, so it has more bulk than a dive skin, but slightly less insulating ability than 2 mm thick sponge neoprene (no trapped nitrogen bubbles).  Polartec is usually worn in warm water, or layered with another garment, where it can be an effective insulating layer.  Dive skins and rash guards are typically made from Lycra,  or other stretch nylon knit, and have NO insulating capacity.  They provide protection from scratches and sun exposure in warm water.  A dive skin worn under a wetsuit can make the wetsuit easier to get on and off.

Terrapin Wetsuits stocks Polartec material for repairs and new custom garments.  We can sew Polartec with thin neoprene for a combination garment as well.  Terrapin does not stock dive skin material.  We are happy to make stitching repairs on your dive skin or rash guard, but for a new garment, we recommend the way-cool skins at www.DiveGoddess.com.


Polartec material has no sponge rubber so does not vary in thickness, and thickness measurements are not specified.

Neoprene thickness is measure in millimeters, but there is no industry standard as to how accurately it is measured, or whether to include the thickness of only the closed-cell sponge or the total sandwich of fabric laminate/sponge/fabric.  The thicker the sponge in the middle, the more the wetsuit manufacturer pays for the neoprene, so there is some incentive to buy 2.5 mm sponge, and then call it a 3 mm wetsuit.  Terrapin orders all our neoprene custom made to our specifications, and we specify the thickness of the sponge layer.  So a 3 mm Terrapin Wetsuit has sponge rubber that’s 3.0 – 3.5 mm thick, not counting the fabric laminate.

The thickness that any given diver needs in order to stay warm under water is based on a combination of factors including water temperature, frequency of repetitive diving, typical dive duration and depth profile (remember neoprene compresses with depth), and body metabolism (as we age, our metabolism slows down and our extremities can get chilled quicker).

Care and Feeding of your new Terrapin Wet Suit or Water Sport Accessory:

Terrapin uses the highest quality neoprene and Polartec materials.  To keep the color and resilience of your new wetsuit or other garment in top condition, we recommend you rinse in fresh water after each dive and air-dry it inside-out and out of direct sunlight.  Do not expose your suit to heat, never put it in a clothes dryer.  After your dive trip is over, or before storing the suit for an extended time, wash in a dilute solution of delicate hand-laundry detergent (we recommend PSI 500 brand or Sink-the-Stink brand wetsuit wash), then rinse thoroughly.  Hang your suit on a wide-shouldered hanger (we recommend and sell Baker Ventilator hangers).  Start the drying with the suit inside-out, and then turn it right-side-out after the inside is completely dry.  Store suits hanging on wide hangers, rather than on narrow hangers or folded, to avoid permanent creases in the neoprene.

Special care notes:


Do this prior to first time use of Polartec material:  Soak your Polartec garment in a non-reactive basin (not aluminum!) filled with a dissolved mixture of 1 C Kosher salt to 1 Gal cold water.  Completely submerge the garment and let it soak for 2 hours.  This will help set the very intensely colored dyes.  Rinse the garment in clear, cold water and hang right-side-out to dry on a wide hanger.

SCS Metal Finish Interior:

Be sure the suit is completely dry before storing or packing.  Avoid storing or packing wetsuits with SCS Metal finish interior flattened against itself.  When hanging garment, ensure there is sufficient room for the garment to have airspace inside.  When packing garment, it may be beneficial to pack it inside out, but protected from any sharp edges of other packed items.  Before putting on the garment after long-term storage or being flattened in a suitcase, reach into the arms and legs of the garments to make sure the sides haven’t stuck together; if they have, pull them open slowly before donning, to make it easier to slide into the suit.