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.
I was a little skeptical b/c I haven't found a good vellum adhesive other than xyron but i only have the small x xyron sticker maker and needed something for bigger pieces. I read the other reviews and this one sounded good. used it for the first time yesterday and it works well. The adhesive does not show through the vellum and seems to hold well. I stuck a whole sheet of vellum over a piece of card stock and used a piece in each corner and a couple on the edges. worked well.