This is great for adhering vellum and it is 99% of the time transparent (maybe once or twice did this show through vellum for me). You'll need a pair of scissors that can get sticky stuff on it (your "secondary scissors" if you will, not your super-prized possession ones). Cut this in pieces & affix to the surface you'll be sticking your vellum onto; do not put on the vellum itself. Peel the backing off the pieces, place your vellum & voila, invisible hold. When I ran out of this recently, I purchased 3L's Vellum Tape just to check out & it was horrible, completely showed through vellum. So I came running back to this tape! This is a go-to product for me.
This adhesive is wonderful to use on vellum. I was kind of nervous about it at first, but there was no reason to be. It was great.
The tape is the best I've used. It virtually disappears so that there is no tape line visible.