Nuphy's GhostBar is made of very high quality plastic -- this is coming from a very picky guy who has been in the hobby for over 10 years. I've used GMK, DCS, MT3 and the likes. I do not use cheap keycaps. The GhostBar provides a very distinct sound profile - even if you use it on a different keyboard without the silicon bar dampeners underneath the spacebar (which comes with Nuphy's Halo series).
It comes in great packaging as well. No warping issues even if it was made from PBT plastic (I bought 3 of them and all were great). The color is very consistent too - unlike other other PBT keycaps that have different sheens in various areas. I love the quality of the product and I'm very happy with the purchase.