The premise needs correcting for a sugar glider
A sugar glider suits no burrowing depth at all, because this small marsupial nests in the air. In the wild, sugar gliders sleep through the day in a leaf-lined hollow high in a tree, curled in a tight group, and a pet glider looks for exactly the same thing: an enclosed, elevated, soft sleeping space. On the cage floor, a thin layer of bedding or a tray liner an inch deep at most serves only hygiene, catching droppings and dropped food that fall through the cage grate. Filling a glider cage with deep substrate would not be used for nesting, and loose material kicked upward can foul food dishes and water bottles that gliders visit at height.
What a sugar glider actually nests in
A sugar glider nests in a hanging pouch of double-layered fleece, a nest box mounted high in the cage, or both offered together. The pouch should be deep enough for two or more gliders to curl inside without spilling out, with the opening sitting above them so body heat stays in the pile. Many keepers hang two pouches so a spare is available on wash day, because a bonded group suddenly denied its sleeping pouch is genuinely distressed. Add a few plain fleece strips inside the pouch for the gliders to arrange. This is where the nesting instinct described in the question actually lives for this species: not digging down, but sealing themselves into a warm, dark, elevated pocket that smells like the colony.
The cage floor and tray, kept shallow on purpose
A sugar glider cage floor works best as a grate over a slide-out tray lined with a shallow layer of absorbent, unscented material or plain paper. That layer's only jobs are to catch waste and make the tray quick to wipe, and it should be changed frequently, because gliders drop food and urinate as they move around the whole cage at night. Deep material in the tray can contact the grate, get pulled through by curious gliders, and introduce fibres and dust into a space that never needed them. Cage placement matters more than tray depth here: gliders need height for gliding and climbing, branches and ropes between levels, and the sleeping pouch hung in the quietest upper corner away from the room's main traffic.
Colony sleeping and what to watch in the pouch
A sugar glider group that has slept piled in one pouch and suddenly splits between two may be signalling a falling-out, heat discomfort, or an unwell glider choosing to sleep apart. Check pouch condition weekly, because seams and hanging straps take constant claw traffic, and a frayed loop can catch a small leg. Wash pouches in unscented detergent and return them fully dry, keeping the spare in rotation so the group is never left pouch-less during laundry. A glider that stops emerging at night, loses interest in food, or feels cold and lethargic in the hand needs a veterinarian promptly, as gliders decline quickly once they look obviously ill. Temperature around the sleeping area deserves care too, since a pouch in a cold draft leaves a group that cannot warm itself the way a deep burrow would buffer other species.
Writing down a pouch-first setup for helpers
A sugar glider's care notes should say plainly that the tray takes a shallow liner only and that the pouches are the nest, because helpers used to hamsters and gerbils instinctively reach for deep bedding. Note which pouch the group currently favours, where the spare hangs, and how often the tray liner is changed, since those details keep a holiday helper from helpfully filling the cage floor and removing the 'messy' hanging pouch to wash both at once. The distinction between hygiene bedding and nesting is the whole answer for this species, and it is exactly the kind of species-specific detail that gets lost between family members. KinsLe Family Sharing records that sugar glider pouch arrangement on the shared profile, so everyone caring for the colony protects the hanging nest first.