Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
Describing the forty days between Queen Blenda's death and his coronation, Kinbote (in VN's novel Pale Fire, 1962, Shade’s mad commentator who imagines that he is Charles the Beloved, the last self-exiled king of Zembla) mentions a so-called patifolia (a huge, oval, luxuriously flounced, swansdown pillow the size of a triple bed) that Charles Xavier had installed in the middle of the Persian rug-covered floor: