In Japan, a shikibuton that is folded away and aired on most days, and turned and rotated regularly, is usually replaced every three to four years. That is a household habit rather than a warranty or a failure point: the filling compresses slowly, and once a shikibuton that started at approx. 10 cm (HIMARI 日葵) or approx. 12 cm (SORA 宙) has settled to around 7–8 cm and no longer recovers after airing, most households in Japan change it.
Why three to four years
Nothing breaks at that point. The filling loses a little loft every night it is slept on, and the loss is gradual rather than sudden. Airing, turning and a firm, level base slow it down; sleeping in the same spot every night, a soft or uneven surface underneath, or leaving the shikibuton down all day speed it up. Three to four years is what that adds up to in an ordinary Japanese home with daily care. Used less often — in a guest room, or as a spare futon — one lasts considerably longer.
The simplest test: measure it
You do not have to count years. After airing, measure the thickness at the spot where you actually lie. HIMARI is approx. 10 cm when new and SORA approx. 12 cm. When that spot has settled to around 7–8 cm and no longer comes back, the shikibuton is doing less work between you and the floor, and that is the point at which a Japanese household would replace it. Lumpy filling, a hollow that stays after airing, or feeling the floor through it are the same signal.
It is worth knowing that some low-cost floor futons are only around 7–8 cm thick when new — the thickness at which a shikibuton in Japan would already be due for replacement. Whatever you are comparing, check the centimetre figure rather than the description.
How to make the loft last
- Fold it away each morning so the underside and the floor can dry.
- Turn it over and rotate it head to foot regularly, so the same areas are not always under pressure.
- Air both sides every one to two weeks in dry weather.
- Use it on a firm, level base; a soft or uneven surface underneath lets it sag.
Heavier sleepers
We publish no weight limit for HIMARI or SORA, because we have no test data that would make that number honest. Any shikibuton compresses more under a heavier body, so a firm, level base and regular rotation matter more, and the 7–8 cm mark is likely to arrive sooner. If you want more cushioning between you and the floor, SORA 宙 is the fuller option at approx. 12 cm. If you prefer a steadier, firmer surface, HIMARI 日葵 has an approx. 8 cm firm polyester support core.