These are folders, not envelopes. They are pretty stiff and hold their shape well. I bet any light card stock would do, but everyone of a certain age has experience with these folders; the fact that they're so basic makes this achievement extra special.
Is age the factor here? feels like they’re just as ubiquitous today as they were when the author was in high school.
I certainly appreciate the idea of crafting something special out of seemingly boring material, but the remark that they were taught to model with this paper in school made me wonder of it does have advantages over basic paper or cardstock.
I think it may be that it's a fairly uniform thickness across manufacturers, whereas if you are getting cardstock from different places you would need to pay attention to paper weights (gsm).
