Layers Atop Leveled Traits

[jeff_wilson]

What GURPS traits can be layered atop other traits that come in levels, like Hardened DR? Any GURPS rules entity may be considered, even if it doesn't have character point costs like advantages, disads, enhancements, or limitations. I suppose rules crunch for gear counts as well, is there some layered CF listing somewhere that can apply to a range of armor DR or weapon damage?

Thanks.