The topper
A topper’s thickness never stands alone. It is added to the mattress height beneath it, and that total, not the mattress height, is what a quilted cover has to reach around. Nine of the twelve topper listings state a thickness, from 1.5 in to 4 in.
The quilted pillow tops filed here state no thickness. They are built like covers, a pocket range turns up in their listings in place of a thickness, and a sum with a missing term is not a sum. The fit check leaves them out and prints the reason.
The eCFR text of 16 CFR Part 1633, the federal open-flame standard for mattress sets, names mattress toppers among the items its definition of a mattress leaves out, and describes them as items with resilient filling meant to be used with or on top of a mattress. It is quoted for the distinction between the terms and says nothing about any listing here.
Titles are loose. Three listings in this category also call themselves a pad in the title or the description, which is why this catalog files by build.