If you run hot at night, you already know the routine. One leg out from under the covers. The blanket pushed to the foot of the bed. The fan on at 3am, and the thermostat blamed for something it may not have caused.

Most hot sleepers never look at the blanket itself. It covers the body for seven to nine hours every night, pressed against skin that is warm and often slightly damp. It gets washed again and again. And for most people, nobody has ever asked what it is made of.

In most homes the answer is polyester. The conversation about microplastics has grown steadily over the past decade, from oceans to food packaging to drinking water. Far less attention has gone to the textiles that sit closest to us: the sheets, throws and blankets we sleep under every night.

This article looks at what the research says about synthetic textiles, why it matters most for people who sleep hot, and what a blanket made of plain muslin cotton does differently.