Reversible fabric can keep you warm or cool

Boston: Stanford researchers have developed a reversible fabric that can keep the wearer either warm or cool, depending on which side faces out. The material could keep people more comfortable in a range of temperatures, and hence help save energy on air conditioning and central heating in homes.

Scientists from Stanford University in the US created a double-sided fabric based on the same material as everyday kitchen wrap. For everyone degree Celsius that a thermostat is turned down, a building can save a whopping 10 per cent of its heating energy, and the reverse is true for cooling. Adjusting temperature controls by just a few degrees has major effects on energy consumption. Our bodies have many ways of controlling our temperature. When it is cold, the hairs in our skin stand out to trap warm air.

Eventually, we may start shivering to produce more radiant heat in our muscles. When it is hot, we release heat as infrared radiation from our skin, and if we are still warm we start to sweat. Water evaporating away from our bodies carries a large amount of heat with it. However, these mechanisms only help within a few degrees. When we get outside the temperature range to which our bodies can adapt, and we reach for the dial on the heating or air conditioning.

Although they were inspired by transparent, water- impermeable kitchen wrap, their new material was opaque, breathable and retained its ability to shuttle infrared radiation away from the body. Compared to a cotton sample, their fabric kept artificial skin two degree Celsius cooler in a laboratory test – possibly enough to stop a person from ever reaching for a fan or the building thermostat. The team is first textile could save a building full of workers 20 to 30 per cent of their total energy budget.

Researchers realised that controlling radiation could work both ways. He stacked two layers of material with different abilities to release heat energy, and then sandwiched them between layers of their cooling polyethylene. On one side, a copper coating traps heat between a polyethylene layer and the skin; on the other, a carbon coating releases heat under another layer of polyethylene. Worn with the copper layer facing out, the material traps heat and warms the skin on cool days.

With the carbon layer facing out, it releases heat, keeping the wearer cool. Combined, the sandwiched material can increase a person's range of comfortable temperatures. With inhabitants wearing a textile like that, buildings in some climates might never need air conditioning or central heating at all. The white-coloured fabric is not quite wearable yet, researchers said.

"Ideally, when we get to the stuff you want to wear on skin, we'll need to make it into a fiber woven structure," said Yi Cui from Stanford. Woven textiles are stronger, more elastic, more comfortable, and look much more like typical clothing. The team aims to create an easily manufactured, practical textile that people could use to save huge amounts of energy around the world.