A stilltent was basically a tent used to sleep in the deep desert of Arrakis. It was usually placed under a layer of sand. The tissue was airtight, so the humidity created inside could be kept and gathered, like a stillsuit or a wind-trap did. This equipment was fundamental in traveling and surviving on Arrakis.
Stilltents are often included as part of a Fremkit.
- https://www.wms.org/magazine/1167/index.html Lessons from Dune, Wilderness Medical Society