I've got two of them somewhere, I'm going to have HWMBLT (ex Physics teacher and his 2nd honours degree is Chemistry ) to have a look at mine and see what he thinks.
I'm with Spamel on this, they're meant to cover trenches and be themselves covered with a foot of soil, there's absolutely no reason for lead. Also, I've got the instructions and there was no mention of the lead. Surely such an "added feature" would be at least worth a word or two.
The tarp is solid, no frills and not lightweight, but it's good kit. The pegs and lines are worth the money on their own.
If you're near Glasgow there is a man sells IPK kits at Blochairn on Sundays, £3 each or two for £5.
cheers,
Toddy