For the purposes of our latest trip up into the Apennines, my base layer consisted of a cotton, polo-neck, long-sleeved top, cashmere and silk leggings and 2 pairs of socks:
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This was then covered with a 200gsm weight fleece and my trusty buff. My trousers have a water resistant gore tex outer layer with an insulating inner layer for parky days such as this one:
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I've found that wearing a wind-stopper makes all the difference, so that goes on next:
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Finally my jacket, also made of gore tex that has a removable quilted lining, balaclava and gloves (with a pair of liners in my pocket, just in case):
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This might seem like a lot of clothes but you can never underestimate the wind-chill factor on a motorbike. Even on a hot day, it's always fresh up there on the back. I think it's colder for me as a pillion because I don't have the engine just in front of me blasting out warm air. On our first couple of trips on the new bike, I was absolutely freezing, and I was quite warmly dressed even then. With this lot on I was comfortable, even if I did look like the Michelin man when I'd finished!