Ordered these with the 6" foam mattresses as they were advertised with them. I thought they would fit the mattress perfectly, however, they are for a regular twin mattress so there is extra fabric to accommodate a thicker mattress. It doesn't create a huge problem though since the extra fabric is easy to tuck underneath and doesn't affect the way the mattress lays on the bed. They are not entirely necessary to purchase with the mattress as the mattress has a nice covering over it already. Good product if you are looking to protect the mattress from allergens like dust mites. Easy to zip on and off.