Yeah, what he said.

Think of the cotton ball as a wick and the petroleum jelly as the wax of a candle. The wax melts and provides the fuel. The wick keeps the flame.

Try a simple expierment. Light a cotton ball soaked with petroleum jelly. Then immediately light a plain cotton ball. The plain will burn itself out in about half a minute. Two or three minutes later, the other is still burning.

If you have oversized tinder or wet tinder, which is more likley to generate enough heat to ignite the tinder? The one with the longer burn time.

Both will work as tinder. The petroleum jelly improves your chances.