Why Is Cotton Flammable?
Because it's a natural fiber.
It is made by sunlight from carbon and hydrogen, like all carbohydrates. It burns quickly because it is finely divided and full of spaces for air flow.
Its a plant fibre made of cellulose, like straw and such. Of course it burns.
EVERYTHING IS FLAMMABLE!even if it is zero everything has a flammability level.and also the melting/boiling point might be higher than the flammability level.
Everything at the atomic level is flammable but at atomic scale the molecules vibrate faster when heat is applied and this heats it and ionizes it or turns it into plasma which is fire