Keeping warm at winter camp

This task is about insulation against heat loss.

Question

illustration: tent and gear
 
a)  At a school camp, on chilly nights, everybody slept in their sleeping bags.
    What is the main way a sleeping bag helps to keep a person warm?

    • Layers of special fibres in the bag create heat.

    • The person's body heat is kept inside the bag.

    • The outer layer of the bag attracts heat from the night air.

    • The bag's outer layer keeps the cold air out.

Question

b)  On a cold day, why do several layers of thinner wool clothing act as a better insulator than a big, heavy, woollen jersey?

    • The heavy clothing causes sweating and the body loses heat rapidly.

    • Thin, wool clothing is more comfortable and is easier to move in.

    • Thick clothing, although it is a good insulator, does not allow the skin to "breathe".

    • Air trapped between the layers of clothing acts as an insulator and reduces heat loss.