Help with fabrics

[humpydumptynumbty]

Can anyone tell me what modal is? Will it make me sweat? I see lots of my tops are cotton mixed with modal (this seems the best you can achieve these days, 100% cotton seems so rare nowadays).
And what about viscose? I don't like it but does it make you sweat? Why do manufacturers use it?

Viscose and modal are (I believe) both semi-synthetic fibres made from cellulose (wood pulp)
Don't have much experience of modal but viscose I like. There are 2 types IME - a jersey that is very light and comfortable and a very different crepey type.