With the arrival of rainy days, waterproof coats are back out of the closets. And with them, another of the comforts we have to thank to the developments of chemistry.

The origin of waterproofing goes back at least to the 13th Century, when South American natives covered their clothes with latex to make them waterproof. Europeans imported the idea, but its success was not immediate: the first waterproof clothes were heavy, uncomfortably hard, and because of the solvente used to spread the latex on the fabrics, they were very smelly.

The development of polymer chemistry of allowed them to become lighter, more flexible and odourless.

But the most remarkable quality of modern waterproofs is that they also allow the perspiration from the skin; that is, they prevent rainwater from getting in, but allow water vapour perspiration to go out.

This effect is achieved by creating structures with tiny pores, through which drops of water can’t get pass, but through which isolated water vapour molecules can.

The modern airy waterproof fabrics are made ​​with two layers of polymers with different properties: a first layer of a micro-porous polymer that is hydrophobic, i.e. it repels water, and a layer of polyurethane, turned inwards, closer to the skin and which is hydrophilic (i.e. it attracts water) and absorbs the humidity that is released from the skin.

Then a bit of thermodynamics come into play: the difference in temperature between the inside and the outside creates the necessary conditions for the water molecules absorbed by the polyurethane to be pushed to the outside.

If you wear a waterproof coat and feel like you’re in a sauna, then it is because you’re still not taking advantage of the developments of the chemistry of polymers.

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