Which Mitten Keeps a Hand Warmest? A Wool, Cotton and Foil Test

Every winter, children argue about whose mittens are warmest. Here’s a way to settle it with data, and to learn what a mitten really does.

The test

Question: Which material slows heat loss best?

You need: four identical jars with lids, warm tap water, a thermometer, a wool sock, a cotton sock, aluminium foil, elastic bands and a timer.

Fill each jar with the same amount of warm water (a grown-up checks it is warm, not hot).
Wrap one jar in wool, one in cotton, one in foil, and leave one bare.
Read the thermometer in each jar at the start, then every 5 minutes for 30 minutes.
Graph temperature against time for all four.

Predict the order first, and write it down.

What usually happens

Wool and thick fabric slow cooling most, the bare jar cools fastest, and foil often does worse than you’d guess, because metal conducts heat easily when it’s wrapped tight against the jar. Your results may differ from expectations, so go with your data.

What a mitten really does

A mitten doesn’t make heat. Your hand does. The mitten slows the heat escaping from your hand into the cold air. Wool, fleece and down trap air in tiny pockets, and still air is a poor conductor of heat.

That also means “cold” doesn’t come in through a hole. Heat flows out. A common mix-up is thinking a hole lets cold in. It’s easier to think of it as letting the warmth out.

Extend it

Test dry versus wet wool. Wet fabric conducts heat away much faster, which is why wet mittens feel cold.
Test one layer versus two.
Compare mittens and gloves. Fingers together share warmth, so mittens usually beat gloves.

The classroom version is Which mitten keeps a hand warmest? in Winter Science. Similar tests are in Which wrap keeps a drink coldest? Sign up for three lessons free.