The following infographic from Rolling Fox provides illustrated...
Knowing that fire-starting is an essential survival skill, most of us have multiple tools for igniting a flame — lighters, matches, ferro rods, and so on. However, even with a powerful blowtorch you’ll struggle to get a fire going if you lack access to highly-combustible tinder. Your tinder material is the substance that bridges the gap between an initial spark or small flame and a healthy roaring campfire.
Char cloth is one of our favorite man-made tinder materials, since it’s easy to ignite, easy to make, and a great way of re-purposing old T-shirts and scraps of fabric. Rather than burning energetically, it smolders and glows with enough persistent heat to ignite wood shavings or dry grass.
Unfortunately, normal squares or strips of char cloth will only last for a short period, and produce a relatively small area of embers. This can make it tougher to ignite more stubborn materials such as damp wood. In the following video, bushcraft YouTuber NW Primate shows how he used twisted strips of cotton to create a denser char cloth bundle with a stronger ember.
In the video description, NW Primate provides some more information on potential issues with this char cloth technique:
As with anything, there are some downsides to this method. On advantage to using flat sheets of cloth is that they sit so nicely on a flat stone, where these pieces of char require a bit more finesse to hold in place without crumbling them. The final product is a bit brittle, so you may find conventional char cloth easier to use during the sparking stage.
This method also uses quite a bit of material, although I only twisted one of the strands that I cut; but if you were in a situation where you were cutting your only t-shirt; it might make more sense to be more efficient and use small squares to conserve the material.
For more instructional videos on fire-starting, knife work, and other bushcraft skills, check out the NW Primate YouTube channel.