The packages generally don't list a bond weight, but in the range of typical papers, the stack in the upper left hand corner of the picture is a heavier bond while the rest is in the mid-to-thin range. All hold a crease well, however.
The only reason I can't use them is that I do modular origami and most of these are either one-offs, or there aren't enough of any given style to complete a model. Hope that helps!
I'm not sure what you mean, or how strong you'd want them to be. If you have a picture or link I'd be happy to try to guess, but they do hold a crease and an origami shape, so I would guess they should.