At 1500 metres the base layer is fine for day hiking but a light fleece layer is needed at night when the temperatures drop to 12–15 degrees.
“You go higher again and when you get up to 2,500–3000 metres, you’ll need the base layer with the thermal layer for daytime travel. You’ll have that plus a waterproof shell when you get higher again, all the way up to summit day when you might have a total of four layers.”
At this point, Tim says, the base layer’s main function is to wick moisture away from your body. The second layer adds thermal insulation. The third layer might include some windproofing, and the fourth layer is the important waterproof layer.
“In the tropics, even at altitude, tropical storms come through in the afternoon.”
High alpine climbing is done at night: “You want to be up and down and back in camp before you get the torrential rain event about 3pm.”
But if they miss this window — the waterproof outer shell is vital protection.
“And when you’re walking in, you certainly have to walk through that afternoon rain to cover the ground.”