Four to six inches: the fancy mouse's working depth
A fancy mouse sits between the true burrowers and the surface nesters, and her bedding depth reflects that middle ground: 4 to 6 inches across the enclosure floor. At that depth a mouse can dig the short, sloping burrows she uses for sleeping and food storage, and still keep her tunnels from caving under her own light weight. Shallower than 4 inches, she can only scratch; deeper than 6, in a typical mouse enclosure, the bedding starts swallowing water bottles' spouts, burying scatter-fed food beyond finding, and hiding her from view for days at a stretch.
Nesting is where the depth really gets used
Watch a fancy mouse with fresh material and you see what the bedding is for. She selects a corner — often inside a hideout, sometimes under a platform — and ferries shredded paper, soft hay, and bedding there in her mouth, trip after trip, then weaves it into a domed, covered nest with a small entrance. Give her a separate mound of shreddable nesting material on top of the 4 to 6 inches rather than deepening the whole floor for nesting's sake. A mouse's nest is a structure she builds upward and inward, not a hole she fills, and loose material she can carry matters more than extra inches beneath her.
Materials a mouse can dig and weave safely
Paper-based bedding suits a fancy mouse on both counts: it holds a short burrow's shape and shreds into nest lining without sharp edges. Add unscented paper strips or plain tissue for the weaving work. Avoid fluffy cotton-style nesting material, whose fine fibres can wrap around a mouse's small limbs and are dangerous if swallowed, and skip strongly scented or dusty beddings — a mouse breathes with her nose in the substrate all day. Aspen is an acceptable base for some keepers, but paper's combination of diggability and nest-worthiness makes it the simpler single choice for this species.
Zoning the enclosure around the deep floor
A fancy mouse's enclosure works best when the deep bedding is the base and everything else is anchored to it. Push the wheel — a solid-surface wheel around 8 inches — down through the bedding so its base sits on the enclosure floor, or it will tilt as she digs beneath it. Set the water bottle's spout height after the bedding is in, not before, because 5 inches of substrate raises her reach considerably. Scatter feeding directly into the bedding turns the whole floor into foraging ground, which is precisely the kind of work this depth is meant to create for her.
Cleaning that respects the nest
The fancy mouse's deep bedding is cleaned in sections, never stripped all at once if it can be helped. Spot-clean the toilet corner — mice often choose one — every few days, and rotate partial changes so roughly a third of the floor is refreshed at a time. When you reach her nest corner, leave the nest itself if it is dry and clean; a mouse whose woven nest is destroyed weekly stops investing in building one, and the nesting behaviour this depth exists to support quietly disappears. Replace the full bed only when odour persists after spot-cleaning, and return a handful of the old, clean bedding so the new floor smells like home.
That section-by-section routine only works if whoever cleans knows which third is due, and KinsLe's Care Teams lets you assign the spot-cleans and rotating partial changes for your fancy mouse by name, each finished job timestamped so the nest corner is never stripped by mistake.