After you consider the pillow packs junk for general useage and ya like fire, I've experimented a bit.
In a former employment our department had easy access to many of what you are calling pillow packs, most likely a Li-poly design. Their weak point is they will heat more during high discharge events and expand/puff up.
So the chip making begins. Open the case, and place outside before in a open area, puncture one of the Li-poly packs (we used exacto knives to do the puncture) and watch the runaway reaction, once started it's very difficult to stop. It will spread to all cells it will be a runaway chain reaction.
It shouldn't need to be said but don't breath the fumes.
