I'll try and describe it...
It's sort of knitted. But machine knitted, so very smooth, not lumpy, and quite thick. It's heavy. Above knee-length, A-line. The ones I have seen have been black with white polka-dots, but the inside is white with black polka-dots. But it's not reversible. It looks a bit stretchy, but I've not been close enough to have a feel.
I did see one in the children's section of H&M, but they definitely come in adults sizes too. They look like the sort of thing you might find in a weird knock-off shop.
I'm not committed to the black and white polka-dot thing, but I desperately do need one of these weird heavy knitted skirts.
Does anyone know what I'm talking about?