From the Library

[Biggles]

Even before dawn the next day the temperature was already at a ferociously high level and the glowing red bail of the sun gave us the impression of some dreadful scourge. We made ourselves face-masks out of linen which we wore under the front of our tropical helmets, hanging down to our chests, with big round holes cut out only for the eyes. Short trousers and sleeveless shirts also proved an agony in the midday heat. Long trousers and long sleeves would have kept off the heat better.   
Seeing the Bedouin going about muffled up to their noses like skiers in a snowstorm, we realised that warm clothing, especially wool, gives protection against heat as well as against cold. That's why in the heat one should put clothes on rather than take them off, but we were not yet wise to these desert tricks.
India The Shimmering Dream  Max Reisch p48