The fabric is nice, smoother than the cotton in some brands, but runs very small.  I wear an 11 in the nylon panties from Woman Within, and that's one size up so they have a little looseness. Can't stand tight clothes :(
Knowing the cotton element might shrink in the wash, and not liking tight undies, and allowing for the fact that the "big girl" sources like Roaman's and Woman Within tend to size generously, I went with 4X, allegedly a 12.  Well, heck, they were so so tight before even thinking about washing them I wouldn't have lasted to the end of my driveway in them.
So factor that in when ordering these.