Charcloth

Char cloth (or charcloth) – also called charpaper – is a swatch of fabric made from vegetable fiber (such as linen, cotton or jute) that has been converted via pyrolysis into a slow-burning fuel of very low ignition temperature. It can be ignited by a single spark that can in turn be used to ignite a tinder bundle to start a fire. It is sometimes manufactured at home for use as the initial tinder when cooking or camping and historically usually provided the "tinder" component of a tinderbox. It is often made by putting cloth into an almost airtight tin with a small hole in it, and cooking it in campfire coals until the smoking slows and the cloth is properly charred.

Char cloth ignites with even the smallest spark, and is therefore commonly used with a flint and steel.

...
Wikipedia