As Ryan O. posted, it is listed, BUT, the titles don't clearly describe the thickness of either product. It is only clarified in the Specifications section of each. And, for some reason, they list them with different units of measure.
The bi-fold 15 pack is 8.5 mm.
The bi-fold 25 pack is 3/16 in. (approx. 4.76 mm)
It would help buyers, if the titles included the thickness.