Mary Gray of Dunedin asks :-

Why do carpets and funiture fabrics fade in the sun?

Ryan McCall, a textile scientist with Canesis, responded.

Sunlight has a lot of energy in it and this will affect things that it hits, you can see this when you get sunburned or when water evaporates on very sunny days. So when fabrics and carpets are exposed to sunlight they are also affected by the energy that it contains. There are not many kinds of coloured things that can stand being exposed to sunlight for a long time without changing. Glass windows filter out most of the ultra violet light that makes dyes fade the fastest. Fading still takes place behind glass but at a slower rate.

When enough sunlight hits the carpet and fabrics the energy affects the dye that has been put in them. This dye is what gives the fabric or carpet its colour and is deeply embedded in the fibres of the material. When enough sunlight hits the dye it disrupts the colour parts (we call them chromophores) that make up the dye molecule and splits them down into smaller pieces that either have no colour or a less intense colour than it had originally.

Different dyes have different resistance to fading by sunlight. We use the most resistant dyes for carpets and upholstery that are expected to last many years, often in sunny conditions. Clothes generally use less lightfast dyes as they are not in the sun as much.