What goes under the sheet, and in what order

A made bed is a stack, and the stack has a logic. Get the order right and every layer does its one job; get it wrong and the expensive layers take the damage the cheap ones were sewn to absorb.

Bottom to top

1. The mattress. The layer you cannot wash and do not want to replace early. Everything above it exists to keep it boring.
2. The topper. If the bed has one, it lies straight on the mattress. Comfort works by contact, so nothing thick should sit between your body and the fill.
3. The waterproof protector. Over the topper, not under it. A spill lands on the top of the stack, and the barrier has to be above whatever you are protecting.
4. The fitted sheet. The washable weekly layer that takes the daily rubbing.

The mistake we see most

Protector on the mattress, topper on the protector. It feels reasonable, the mattress is the costly part, but it leaves the topper bare. Foam and fiber fill soak up a spilled coffee faster than any mattress would, and a soaked topper dries slowly and unevenly. If you protect one layer, protect the top of the stack.

The pillow stack

Same idea, smaller scale: pillow, then a zippered protector, then the pillowcase you actually see. The case takes the face contact and goes in the wash weekly; the protector under it keeps the fill clean for years and only needs the drum once a month or so.

One practical note: put the protector on so the zipper ends up at the outer edge of the pillow. You will find it faster on wash day.