A bed is a stack of decisions, and most of them turn out to be laundry decisions wearing other clothes.
Where to start
Why treat the bed as a system?
Because every layer changes what the layers under it have to do, and swapping one without the others is why beds stop working.
Put a heavier duvet on and the sheet underneath matters more. Drop the wash temperature and the pillow protector has to work harder. Nothing in a bed is independent of the rest of it.
So this is organised by the job each layer does, not by the aisle it was bought from.
Does thread count mean anything?
Almost nothing above roughly 400, where counting methods diverge enough that two labels stop describing the same cloth.
Weave, fibre length and finishing do the work people credit to thread count. Those get their own pages here, with the trade terms explained rather than dropped.
What gets covered?
Four things: what the layers are, how they go together, how they are washed, and how long any of it should last.
Percale, sateen, linen and flannel, and what each does on a hot night.
Building a bed for a season, and the top-sheet argument itself.
Water temperature, detergent chemistry, and the case against fabric softener.
Drying, storing, rotating, mending, and when to admit a sheet is finished.
Latest guide
What is the difference between a flat sheet and a fitted sheet, and do you need both?
A standard American sheet set comes with one of each. Folded on a shelf, they look alike. They do different jobs, though, and each one goes wrong in its own way when you buy the wrong size or put it on the wrong layer.