Strand-to-strand adhesion. A matchstick is a wide bundle that has 3 to 4 times as many filaments in it as do the majority of the bundles in the bed.

when fibers burn completely back and don't fuse together at all, the result is commonly called "matchsticks" because the end of each fiber now looks like a matchstick. This is usually due to having the fusion current set at a high level.