Wladimir,
I use covering paper for painters, it's a recycled paper, stronger than the typical wrapping paper. It comes in different weights, but I am using paper from 85 gr/m2 to 136 gr/m2. I tried every kind of paper I could lay my hands on and choose this one because it was the strongest and also when I cover it with plastic film the foam doesn't show through.

Schpankme
Yes I would like to make it lighter, but this is the floor of the pipe tunnel. If I cut more holes I don't know if the paper would isolate the heat from the pipe.

Sig