The
System
Think of the core as a mattress and the cover as the sheets: you wash the sheets and keep the mattress.
The stone nest is built the same way, in three parts. The foam core stays for good. The liner and the cover come off, wash, and can be replaced on their own.
The stone and the nest
The name describes the two halves. The stone is the foam core: the structure and the shape, the part that stays. The nest is the liner and the cover: the soft, washable part your dog lies on.

The core stays
High-resilience foam, cut from block foam, with its rounded edge built up by hand. It sits under the liner and the cover, and it's the part that does all the supporting.
It's also the one part we don't sell on its own, because it isn't meant to be replaced.
The layers change
The liner is a waterproof fitted sheet, white, with no zipper. The cover is the upholstery, in every colorway, with a zipper around the base. Both come off, both wash, and both are sold on their own in every size.
A worn cover, or a change of color, means a new cover rather than a new bed.
The palette across the room
The pillow cover is cut from the same fabric in the same colorways, in three sizes, so the bed and your sofa look like one thing.
The core stays and the cover changes.