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 It stays unpublished until legal review and source verification are complete.

The answerThe common misunderstanding is that a sudare is decoration, or a curtain substitute. It is an external shading device: hung outside the window, 10–20 cm from the glass, it blocks 50–80% of solar heat before it enters, whereas an internal curtain only stops light after the heat is already inside the room. Field measurements report room-surface temperatures several degrees lower and air-conditioning electricity 10–20% lower behind a sudare or green curtain. Hang it outside, leave a gap for air, wet it on the hottest afternoons, and take it in before typhoons.

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

Sources

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

What do people get wrong about sudare, the Japanese summer blind?

Sudare, yoshizu and the numbers

Sources

About this article

Sources

Related questions