Once the bow is glued up in blank form, it feels very heavy, but after the shelf is cut and it is shaped it is not too much different. Just slightly noticable and I like the heavier riser. I would guess it adds about 4 ounces to the overall final weight of the bow.
It is terrible to work with though. It is hard to get ideal fades and it takes me easily twice as long to do anything to the riser....shape it, sand it...cut it....its hard as a rock. Also, prior to the application of thunderbird I use 3 4 light coats of tru-oil to seep into the linen fibers in order to get a jet black finish. Otherwise, if you go straight to spraying, the thunderbird will sit right on top of the phenolic (and not penetrate to get that nice jet black color).