Cotton clothing may be widely seen as being kind to the skin, but not in the mountains where it can kill, the Mountaineering Council of Scotland has warned.
Man-made synthetic fabrics and wool are the climber's best friend, even for underwear, according to the experts in mountain safety.
That is the stark message going out to those taking to the hills as part of a bid to stop people freezing to death. Each winter people die of exposure and hypothermia in the Scottish mountains.
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Heather Morning, Mountain Safety Adviser with the MCofS, said that wearing cotton clothing can significantly increase the risk of developing hypothermia in winter conditions, and sometimes in the summer as well.
She said that when cotton clothing gets wet, whether through rain, snow-melt or sweat, it provides no insulation and will quickly cool the skin.
She said that man-made synthetic fabrics or wool 'wick' moisture away from the skin and retain warmth even when wet or damp.
"As soon as somebody becomes stationary on the hill and they are damp because of sweating, rain or snow, then they get very cold very quickly," she said,
She said that many who weren't experienced climbers might not see it is a problem.
"I have people who turn up for winter courses wearing jeans, and they are horrendous when wet as they just sap warmth from the skin."
But she said the onset of hypothermia usually had several causes, and inappropriate clothing was only one factor. Eating adequate and appropriate food was also important.
"Carbohydrates of both the slow and quick release varieties are best for fuelling a day on the hill. A great start would be a bowl of porridge."