It's used when installing midbass drivers in doors to seal the baffle in the door panel. Non hardening is used because it alows it to stay squishable and move and stuff. It's not required, but is said to help a lot with SQ..
Thanks, so you use this to seal those foam XTC baffles? I planned on getting those baffles as well, but didn't know you had to seal them...Good info, thanks again...