As many Canberrans will attest, thermals make up an essential, if not stylish, component of a winter wardrobe, especially if you want to spend time outdoors.
We lose body this heat in a number of ways. These include conduction, where heat is transferred from a warmer solid object to a cooler solid object - anyone who has sat down on a metal bench in winter will have experienced this first hand (or first backside).
Convection is where heat is transferred from your body to a liquid or gas, as experienced on a windy winter day, or more happily, when you dive into the pool in summer.
Evaporative cooling is where the process of a liquid changing state into a gas takes energy (in the form of heat) away from its surroundings.
Fleecy jumpers work as insulators, or convection-heat-loss fighters. They keep the air that is sitting close to the skin in place, so that once your body warms it up, the pesky wind won't blow it away, and the rate at which it leaks out into the cool outside air is slowed. Double glazed windows work on similar principles.
The word ''loft'' can be used to describe how thick the insulating air space created by clothing is. Puffer jackets trap lots of air, so they have a high loft, and keep you warm.
So where does super-thin thermal underwear come into the picture?
Although thermals provide some insulation, their main job is to fight evaporative cooling. Here's a quick test that allows you to observe evaporative cooling first hand. Blow across the back of your hand, then lick it, and blow again. The wet hand should feel much cooler. This is because as the water evaporates, it draws energy (in the form of heat) away from your skin. Thermals ''wick'' (or draw) sweat away from the skin, minimising evaporative cooling.
Wool, wool-bamboo blends and synthetic fabrics like acrylics have excellent wicking properties, and make great thermals, or ''first layers'' in your quest to keep dry and warm while working outdoors. Wool can absorb more than 30 per cent of its weight in water before it starts to feel wet.
Response by: Alice Ryder, Fuzzy Logic
The Fuzzy Logic Science Show is 11am Sundays on 2xx 98.3FM.
Send your questions to AskFuzzy@Zoho.com Twitter @FuzzyLogicSci Podcast FuzzyLogicOn2xx.Podbean.com
