Cotton balls catch easy fire. Cotton balls soaked in petroleum jelly keep easily fire. Below you can see a comparison video of two similar sized cotton balls. One of them is soaked in petroleum jelly. The regular one burns only for about 1 minute (even a little less) and the one with petroleum jelly burns almost 5 minutes.
Having some cotton balls in your fire starting kit is great, having a petroleum jelly cotton ball in it is even better!