B-10 Pocket Lining Material?

Hi all,
not really a new member, just had to rejoin.

I have an ATF B-10 and the pocket lining is something other than cotton twill. Can anyone tell me what an original B-10 pocket lining material is?

Also what are the problems with the ATF B-10 versus an original, lining, sleeve girth, ...?

Thanks, Jeff