A way to determine the fiber composition of a fabric is by burning a small piece and then examining the smell of the smoke, the behavior of the flames and the appearance of the ashes. Then compare those factors to a chart of known fabric burning behaviors to determine the specific content of the fiber.
the following is entered by someone else:
cotton burns like paper and smells like burnded paper, so does viskose as it is made of cellulose.
i dont know about bamboo, cos back in my school days that material was not “en vogue” but i can imagine it burning just like cotton.
wool smells like burnt hair or nails cos of the keratin content. it burns slowly (thats why you can use a wool blanket to kill a small fire)
synthetics (nylon, acryl, polyester,…) smell horrible and burn in the nose, and melt together to a lump of plastic.
i have learned this 15 years ago in fashion school and dont remember much more anymore.