I assume you're talking about abs, as in door panels? If so I use 1/8 for most panels and usually staples just fine. Once in awhile I'll get a piece that seems to be a lil harder than normal and it will reject staples. When this happens I simply lightly run the heat gun over it for a bit to soften it up. IT DOESNT TAKE MUCH! As for 1/4, I don't really use 1/4 abs much but when I have, same thing applies

Thank Michael