Stacking hills

[cameronian]

My Kallistra hex hills stack beautifully.

[Wulf]

In a similar vein, has anyone used Kallistra's non-slip backing sheet? How thick/tough is it? I use individually based 10mm minis on 12mm washers, and I've stupidly based them smooth side down (punched washers have a smooth side & a ridged side, like punched boardgame counters). I intend to use a 12 or 10mm punch to punch out circles, if that'll work.