This is exactly what we use for waterproofing our fireworks before a display. It's clear so you can still see through it, we like to also use a fluorescent post it notes where the fuse is so we can see it clearly. These are extended core rolls meaning very easy to hold while wrapping, something again we find much easier.
The price is for a single roll which is 40cm wide and an incredible 300m long so lasts for ages!
We wrap our cakes in both directions meaning a double layer of protection. The fireworks will easily burst through the plastic but if you get worried simply remove it before firing.