Why do hairdressers use tin foil when dying someones hair?

Why do they use it? Does it do something like help the colour show up?Why do hairdressers use tin foil when dying someones hair?
You can do different coloured highlights, it gets the pieces of colours exactly where you want them, also it doesn't hurt.


Also they are good at heating so your hair can take to the colour easier.Why do hairdressers use tin foil when dying someones hair?
They mostly use it to keep the colored hair seperate from the non colored hair...
It keeps the hair seperated from the rest and it stays in place easier. It is also a heat generator
radiates heat.