El­lis Brigham: truth about wa­ter­proof

The Oban Times - - OUTDOORS -

THERE’S no such thing as wa­ter­proof.

I was taught this by a Scot­tish moun­tain guide. As much as I wish it wasn’t true, it is.

Wa­ter­proof­ing cloth­ing is tricky. If you make a jacket out of plas­tic, it will not be breath­able. If it is not breath­able, then the sweat you gen­er­ate on the inside of the cloth­ing con­denses and you get wet any­way.

The way that most mod­ern wa­ter­proof gar­ments are made is with a very thin mem­brane of PTFE (poly­te­traflu­o­roethy­lene – no, I can’t pro­nounce it ei­ther).

This is a ma­te­rial which al­lows wa­ter vapour to pass through freely but will only al­low liq­uid wa­ter through un­der ex­treme pres­sure. This pres­sure is mea­sured as if you got a piece of ver­ti­cal drain­pipe with the mem­brane cov­er­ing the bot­tom and poured wa­ter in the top un­til it started to force its way through.

As a gen­eral rule, any­thing less than 10,000mm is not suit­able for moun­tain use.

If you use Gore-Tex, de­pend­ing on which type, it can be rated at 28,000mm mean­ing that there’s 28 me­tres of wa­ter be­fore it forces its way through. This seems un­nec­es­sary but when all-day rain is con­sid­ered and a heavy ruck­sack is worn or you sit against some­thing, those pres­sures can be cre­ated.

Other tech­nolo­gies are avail­able and suit dif­fer­ent uses. Ul­ti­mately, the best thing I can say, is find out what works for you, ask staff in store to ex­plain your op­tions ... or just don’t go out when the weather is bad.

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