Tinder is a natural material usually of biological origin. The distinctive feature of this material is its ability to easily begin to smoulder, even upon contact with a small spark. In fire making, the most common types of tinder used are either natural or made of scorched flax or cotton fabric – also known as char cloth. Natural tinder is made from a polypore fungus which grows on the trunks of dead birch trees, or it can be made by scorching pieces of natural material in a closed metal tin and in the absence of oxygen. In the past, other ways of preparing tinder existed, but these are rarely used today. So, one material that easily catches sparks is dry, rotten wood. You can restock your stores of this kind of tinder by finding a crumbling, rotting tree stump in the woods.