Just reading about rain traps in Ray Mears' Essential Bushcraft. He warns "Avoid canvas tarpaulins or tent fly-sheets that have been treated against decay or may be tainted".
What does he mean by that? How does one find out if they've been treated against decay or tainted?
I use a tarp cut out from the ground sheet of an old tent and planned to try a rain trap with it. But am now rather hesitant...
Any elaboration/advice would be great, cheers folks.