I don't use vaseline on mine, mostly because I didn't have it when I started making them. I use Crisco shortening because it comes in a huge can. Seems more cost effective to me.
Anyhow, I have tested the ones I make by saturating them with Crisco, then submerging them in a glass of water for twenty minutes. I pulled them out, wrung the water out, and lit them with matches. I couldn't get a ferrochromium rod to catch on them (big suprise, huh?). I found that if I fluffed them out into a teepee sort of shape, then lit the bottom, the flame would dry out the upper part as it burned. Even thoroughly soaked, they are better than alot of the stuff you could find on your own in the woods. That is about as good as I can expect.
BTW - Even the saturated greased cotton balls catch a spark very well when dry. A whole cotton ball will burn for about 5 or so minutes with a flame about six inches high. It works for me.