Used on its own or blended with rubber, cork makes an excellent gasket material. It’s flexible over a wide temperature range and very compressible. It resists oil, it’s fire-resistant and it doesn’t creep. Why then, do some gasket and gasket material buyers express concern when presented with it?
The answer is, in some quarters there’s a perception that cork absorbs water. Does cork absorb water is a frequently asked question. If this were true, wine bottles would leak when laid horizontally, but it’s not entirely incorrect either. For an explanation, let’s delve into the properties of this natural material.
The Structure of Cork
Cork grows on trees, and like all biological materials, is composed of cells. As a paper from North Carolina State University (NCSU) noted in 2015, the cells in cork contain air, so it can be considered a closed cell foam. (“The rationale behind cork properties: A review of structure and chemistry” Pereira, H. (2015).)
This similarity to a sponge material is probably the origin of the belief that it absorbs water, but there’s a bit more to it. The NCSU paper notes that, “The porosity coefficients of cork range from below 2% to over 15%”. Or in other words, it will absorb a little water. This occurs at the cells that have been cut open on the surface and also through defects in the cell structures.
Countering this though, the cell walls are made mostly of a substance called suberin. Naturally hydrophobic, this repels water, which works against absorption.
So, as a conclusion, yes, cork can absorb water, but the amount is very small. It’s not a sponge.
Relevance to Gasket Materials
Natural cork, often described as composition cork, can be used for gaskets. More often, it’s blended with a synthetic rubber like neoprene, nitrile or silicone. This increases strength and flexibility while enhancing oil resistance.
Thanks to high compressibility, cork-rubber blend gasket material works well on uneven surfaces and in low pressure applications. It’s available in thicknesses from 1/32” to ¼”, can be die, water jet or laser cut to shape, and no, it won’t absorb water – to any significant degree.
