I felt like I was taking a risk when I ordered these for my costume, but I had enough time to buy something else if it went wrong.  Thankfully it didn't!  These ended up just perfect.  I needed something cute but enough to cover my bottom.  These really will fit many sizes.  They are made with what's called "shirring", which is a way of sewing elastic on back of the fabric so that the fabric gathers up.  It allows it to be stretchy, but with texture.  This way, they can be snug, but without looking skin-tight.

I'm maybe an 8-10, depending on the clothing.  These fit just fine and there's even room for a few sizes up.  I'm hesitant to say how many sizes, exactly, but I'm certain a 14 could also fit into these and perhaps a bit higher.  The stretch is from side to side, so they may not scale up as well as far as covering the bottom of the cheeks for larger sizes.  They cover mine just fine, though.

The base fabric is a white lace, and there's a lace-look edging on the top of the elastic at the waist.  It's soft enough to be by the skin for extended periods.  The seams are strong and the thread is a soft thread and there's a small bit of soft cotton crotch lining, so if you want to wear these without anything under them, it should be comfortable.  The bows are of satin ribbon.  The lace over the rest of the garment is a slightly stiff lace.  I wouldn't call it rough, but I wouldn't want it against my skin all day, either.  It is just stiff enough to keep its shape, and no more, which is good.  I think they found just the right balance.  The only place this lace will be near the skin is at the leg openings.

Overall, I couldn't have asked for a more perfect pair of pettipants.  Great value.