Not long ago I linked to a method of storing/carrying the cotton ball/petroleum jelly firestarters I hadn't seen before: fire straws. Very good idea, and I made some up to try.
And today I remembered to actually take one out and actually try it, using a magnesium block/striker to light it.
First thing: you need something with an edge to cut it open(ever tried to twist a straw apart?) You might be able to beat one between two rocks to shear it open, I'll try that later.
Second: I'd had this one
sitting around for a while, including in a hot area; no leakage of the jelly. I nipped it open in the middle and just pulled one side partway out, stubbed it like I was putting out a cigarette to fluff it a bit, and hit it with sparks; lit right off.
I was curious as to how it'd continue; as it burned the straw melted/burned along the top and the cotton continued burning nicely.
I forgot my watch so no exact time; I'd say this had been burning for about three minutes when I put it out. Three minutes of heat to light your tinder or kindling... that's enough to dry out damp stuff and get it started.