I’m not sure if the science of it, but I find cotton to be much more comfortable. Synthetic fibres get really sweaty while cotton feels comfortable in all weather. And I use to have skin issues (eczema and psoriasis) and cotton was defitnely less irritating than synthetic fibres.

My fave is merino wool leggings, very soft and good at regulating body temperature. Doesn’t get too hot but also protects from the cold.