In the Elastomeric Industry (the companies that manufacture rubber for various uses), the technically correct term for closed cell sponge rubber is expanded rubber. The cells are like individual balloons, holding the gas and not allowing moisture to pass through as long as the cell wall has not burst. The chemical compound for expanded rubber may be the same as solid rubber (like O rings and gaskets). There are three types of rubber used in wetsuits: either Latex Natural Rubber (NR), synthetic rubber neoprene made from isobutylene (BR), and synthetic polychloroprene made from limestone/calcium carbonate (CR). The solid rubber compound is mixed with a "chemical blowing agent" to create the sponge cells. 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 whichich 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 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 a sponge that has been cured to have smooth skin inside and outside. Such suits are used primarily by competitive swimmers and free divers because it is believed the texture is more hydrodynamic. Some wetsuit companies have misused the term to differentiate their product from their competitors, claiming 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 (hard rubber). Permeability connects pore spaces from one side to the other, allowing 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 completely, compromising the integrity and insulating ability of the material. The degree to which the material will rebound after a deflection and the percent to which the material will stretch without tearing the cell walls are properties that can be controlled when manufacturing the sponge rubber. These properties are discussed in ASTM D1056, ASTM D6576, and Mil-R-6130C. Companies that manufacture neoprene sponge rubber 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 wetsuit material's attributes, 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). It is more likely to rebound to its original thickness after repeated or severe compression than the Neoprene-Butyl blend rubber. However, blended rubber generally has a greater capacity to stretch without tearing the cell walls than 100% Neoprene. Terrapin offers Glomex Neoprene-Butyl blend rubber and Yamamoto calcium carbonate-based CR Neoprene (made from limestone). Yamamoto says their rubber has a 23% higher close cell structure than petroleum-derived neoprene, making it more buoyant. It also has a maximum elongation of over 480%, whereas 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.
  • Greenprene is a trade-marked name for one company's CR Neoprene, made from calcium carbonate.  Several companies market wetsuits made of CR neoprene under various different trade marked names.
  • Aquaprene is a trade-marked name for one company's neoprene where the glue used to laminate the fabric to the sponge is water-based, rather than solvent-based.  This technology reduces manufacturing VOC's but is relatively new, so unknown how the material will hold up after repeated use under water.
  • Insta-Dry is a 3-stack laminate: outer skin 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.
  • SCS coating (Super Composite Skin) Nano coating made by Yamamoto-Bio.  Yamamoto's testing shows it "reduces dynamic friction by over 99%".