What do people get wrong about sudare, the Japanese summer blind?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
Before air conditioning, Japanese houses kept cool with a hanging reed screen — the sudare — and its stand-up cousin, the yoshizu. They still sell in every home centre each June for a few hundred yen, and studies by Japanese utilities and universities keep finding the same thing: a shade outside the glass beats any curtain inside it.
Sudare, yoshizu and the numbers
| Item | Detail |
|---|---|
| Sudare | Hanging blind of split bamboo or reed (now often plastic), rolled up and down; 88 × 180 cm ≈ ¥500–1,500 at home centres. Hooks clip to the window frame or balcony rail |
| Yoshizu | Free-standing reed screen (2–3 m tall) leaned against the eaves or veranda at an angle; shades a whole wall and doorway. ¥2,000–5,000 |
| Where | Outside the glass, with a 10–20 cm air gap. Inside, it still cuts glare but most of the heat has already come through |
| Effect (reported) | 50–80% of solar radiation blocked; interior glass surface 5–10°C cooler; room air 1–3°C cooler on sunny afternoons; air-conditioning use down 10–20% in utility and university trials |
| Comparison | Interior curtain: ~30–40% heat reduction. Exterior shade (sudare, awning, green curtain): 60–80%. Reflective film: 30–60% but permanent |
| Uchimizu | Wetting the sudare (or the ground) in the late afternoon adds evaporative cooling: the air passing through drops 1–2°C |
| Care | Roll up in rain if possible; bring in before typhoons (they become sails); brush dust; natural reed lasts 2–4 seasons, greys with UV |
- Which windows: south and west — the west-facing afternoon sun is the one that heats bedrooms for the evening. North-facing windows don't need it.
- Ventilation: a sudare lets breeze through and hides the interior — the traditional way to open windows in dense neighbourhoods without being seen. It's why Kyoto machiya still hang them.
- Balconies: attach to the balcony rail with S-hooks or ties; check your building rules — some ban anything on the exterior. Renters: no drilling; use tension poles or rail hooks.
- Green curtains (bitter gourd, morning glory on a net) are the living version and give the same shading with higher humidity and a crop (see the balcony gardening article).
- Modern versions: aluminium-coated sunshade screens, awning cloth on a tension pole — same principle, longer life, less charm.
- Winter: take it down; you want the sun.
[Verify] Percentage reductions in solar heat and air-conditioning use come from utility/university trials cited in METI and MOE materials; confirm the specific figures before publication.
---
Sources
- Ministry of the Environment — "Cool Choice" summer measures: exterior shading (sudare, green curtains) and energy saving
https://ondankataisaku.env.go.jp/coolchoice/
- Agency for Natural Resources and Energy — Household energy-saving guidance (window shading, air-conditioning)
https://www.enecho.meti.go.jp/category/saving_and_new/saving/
- Tokyo Metropolitan Government — Heat-island countermeasures: uchimizu and shading trials
https://www.kankyo.metro.tokyo.lg.jp/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
Always follow the instructions on any product you use, and never mix cleaning products. If you rent your home, check with your landlord before making any changes.
Sources
Tell us if this has changed
Approved contributions keep the contributor's name, shown in five languages.
Related questions
Other languages：日本語 ／ 简体中文 ／ 繁體中文 ／ 한국어
Value Village is not a government body. Always confirm procedures on the official site.
Written by Value Village from public sources. Nothing here is reproduced from another site.