If a fitted cot sheet pops off at the corners or wrinkles through the night, it’s usually a fit, depth or layering issue. Use these fast checks and fixes to keep the sleep surface snug and safe.
Fast check (30 seconds)
- Corners wrapped? Elastic pockets must tuck fully under all four corners.
- Flat surface? No slack or ridges through the centre.
- Layers? If using a protector + sheet, both must fit tightly (no bunching).
Common causes → fixes
1) Sheet too shallow or too large
Sign: Corners lift during movement; centre looks loose.
Fix: Re-measure length × width × thickness. Choose a sheet that fully wraps under. See: Cot & Bassinet Sheet Size Guide (AU).
2) Slippery or bunching layers
Sign: Protector shifts under the sheet; two layers slide.
Fix: Use a grippy, firm-fit protector—or simplify to a 2-in-1 waterproof fitted cot sheet so you’re only changing one layer.
3) Corners fitted in the wrong order
Sign: One corner keeps popping off when the last corner is fitted.
Fix: Fit one long-side corner, then the opposite long-side corner to create tension, smooth the middle, then finish the last two corners.
4) Mattress height changed (thicker topper)
Sign: Sheet used to fit, now rides up after adding a topper.
Fix: Size up pocket depth or remove the topper (follow safe-sleep guidance for firm surfaces).
5) Tired elastic
Sign: Elastic looks stretched or wavy.
Fix: Retire the sheet. Preserve elastic by washing gently; full care steps here: How to wash waterproof bamboo cot sheets.
Quick re-fit routine
- Seat the first corner fully under the mattress.
- Fit the opposite corner on the long side to set even tension.
- Smooth the surface, then fit the remaining two corners.
- Do a middle “pinch test” — you shouldn’t lift excess fabric.