Yes for the most part. There are some that are somewhat translucent, like pearl but the darker colors are opaque. They are usuallly shiny.
The main thing that Inoticed about bitters made with them is that they did not scare the bones like most of my gotchas. Maybe it was the design, but I think the weight had something to do with it.
There is a product catering to fly fishermen called E-Z Shape sparkle body. They have a few colors that you cannot get in most fabric shops, but the charge three to 4 times as much. I like their Shrimp, Sand and Pearl for making gotchas and bitters