Look on the front page of Toplace, go down to the bottom right corner, click on the triangle & use the drop down boxes...those are your choices right there. The TL400 poly skin bases are injected Regards-M
Knots are only done on lace bases... imagine the lace magnified many times..it`s like a fisherman`s net... the hairs are tied in a knot onto each link .. any of the poly/skin materials are either injected [machine] or looped .... I think looped can tend to shed faster than other attachment-types. Regards, Paul.
Just as a note: You can get CUSTOM skin pieces that are knotted. If you're working with SUPER think material (.02mm) or less, it's a good technique for keeping the hair from shedding. If the knots are small enough, they're not noticeable.