Overshot Card/Wads for PBBA 20 Gauge

For those of you who make your own overshot cards or wads for air shotguns, I was just wondering what material you prefer.

When buying premade wads, I liked the Ballistic Products N720 to keep the shot from pouring out, and then capping with the NC20:

https://www.ballisticproducts.com/125-Maxi-Nitro-Card-500_bag/productinfo/NC/

The NC720 is very dense, tight, and offers some back-pressure that seems to give the shot more power when compared to lighter materials. Now that cards are hard to find, I'm punching my own and am looking for something similar to the Nitro Card (NC20). The description just says it's made from .125" "specialized industrial board materials." They look a bit like masonite without the textured backing.

Any suggestions, preferences, or experience would be much appreciated.


 
Thanks for the suggestion, Nathan. I did try posting it there as well. It's a good idea as some of those guys may know what that particular material actually is. I just thought maybe someone here had a similar experience with the PBBA. In my powder shotgun experience, adding back-pressure to a shotgun shell with wadding has never been something we needed to consider. The closest thing there was adding a roll crimp when seating a bullet to a handgun or rifle cartridge to add a bit of it. 

BTW, word is that PBBA has a new 20 gauge on the way. Can't wait to see what Terry brings us next. 👀