SteamPressClear

How does a steam press work?
Two thousand watts into a thick metal plate, a strip of two metals that clicks it on and off, and a few drops of water that flash into steam. Take an iron apart in 3D, see why steam unlocks a crease, and meet the laundry's boiler press and the istri-wala's charcoal iron.

▶ Play with it  ·  Read the 60-second explainer  ·  Watch the 40-second video

In 60 seconds

1. A hot plate, a thermostat and some water. A steam iron is a thick aluminium or steel soleplate with a heating element cast inside it, a bimetal thermostat under the dial, and a water tank whose drip valve lets drops fall into a steam chamber on the hot plate. At 2,000 W it draws about 8.7 A from a 230 V socket.
2. Steam unlocks the crease. Cotton and wool chains are held in a fold by hydrogen bonds. Water slips between the chains and heat lets them slide above their glass transition; the iron's weight presses them flat. As the cloth cools and dries, the bonds re-form and lock the flat shape in. Polyester needs only heat, but melts if it is too hot: hence the care label's one, two or three dots, up to 110, 150 and 200 °C.
3. The heat sums. The soleplate stores about 620 J per degree, so 2,000 W brings it to 200 °C in about a minute. A brass-on-invar strip curls about 2 mm as it warms and clicks the element off and on. Turning tap water into steam takes about 2,550 J a gram, so a 2,000 W iron has heat to spare for only about 40 g of steam a minute.
4. The laundry's boiler press. A small boiler at 4 bar holds water at about 152 °C. Its steam blasts out about 1.5 g a second, arrives hotter than 100 °C and dry, and the hot water stores enough heat to flash into about 100 g of steam per litre. A pressure switch, a gauge, a sight glass and a safety valve keep it in check, and a vacuum table pulls the steam through the cloth and then cools it in seconds.
5. The istri-wala's charcoal iron. Five kilograms of cast iron store about 2,300 J per degree, so the istri-wala's box iron stays hot between loads of charcoal; blowing on the coals gives them more air and more heat. Burning charcoal makes carbon monoxide, so it must never be used in a closed room.
6. Safe and lasting. A gram of steam condensing on skin gives about ten times the heat of a gram of boiling water. Never leave an iron face-down, switch off and unplug when you step away and before filling, use an earthed socket, and never tamper with the thermostat, thermal fuse or auto shut-off. Hard water leaves limescale that clogs the steam holes.

Words worth knowing

Term	Meaning
Soleplate	The flat metal bottom of an iron that touches the cloth, with the heating element cast into it.
Thermostat	A switch, here a bimetal strip, that turns the heater off when hot enough and on again as it cools.
Bimetal strip	Two metals bonded together that expand by different amounts, so the strip bends when heated.
Latent heat	The heat that turns water into steam without changing its temperature: about 2,257 J for each gram.
Hydrogen bond	A weak pull between neighbouring molecules; in cotton and wool it holds the chains in shape.
Glass transition	The temperature above which a solid's long chains can slide, so it softens and can be reshaped.
Gauge pressure	Pressure above the air outside, the number on a boiler's pressure gauge.
Safety valve	A valve that opens by itself if a boiler's pressure climbs past its limit. It must never be tampered with.
Carbon monoxide	A poisonous gas with no colour or smell, made whenever charcoal or other fuel burns.

A short history

Two thousand years from a pan of hot coals to a solar ironing cart.

• 100 BCE · Pans of hot coals smooth cloth (Unknown makers, China)
• 1600 · The sad iron (Blacksmiths and households, Europe and North America)
• 1871 · A cool, detachable handle (Mary Florence Potts, Ottumwa, Iowa)
• 1882 · The electric flatiron is patented (Henry W. Seely, New York)
• 1890 · Mumbai's Dhobi Ghat is built (Dhobis of Bombay, Mahalaxmi, Mumbai)
• 1904 · A steam pressing machine for tailors (Hoffman Pressing Machine Company, Syracuse, New York)
• 1905 · The iron with the hot point (Earl H. Richardson, Ontario, California)
• 1926 · The first steam iron on sale (Eldec, New York)

The full story, with 22 moments, charts, people and 21 sources: glassbox.how/e/steampressclear/history. The data lives in history.json.

Video and slides

Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.

File	What	Size
glassbox/reel.mp4	Reel / Short, with captions and soundtrack	1080×1920
glassbox/video.mp4	YouTube video, with captions and soundtrack	1920×1080
glassbox/slide-1…10.jpg	Instagram carousel	1080×1350
glassbox/thumb.jpg	YouTube thumbnail	1280×720
glassbox/cover.jpg	Share card and repo social preview	1200×630
glassbox/history-reel.mp4	“History in 10 moments” Reel / Short	1080×1920
glassbox/history-slide-*.jpg	History carousel	1080×1350
glassbox/post.json	Post copy and schedule used by the publish kit

Privacy

This box has no accounts and no ads, and it ships its own fonts and libraries. When you run it yourself it sends nothing anywhere. On glassbox.how, the site's /bar.js also loads Glassbox's analytics: Google Analytics to count visits (it asks first in the EU, UK and Switzerland, and stays off when your browser sends Global Privacy Control or Do Not Track) and ClickTrust to detect bots.

It remembers a few things in your own browser only, and never sends them anywhere:

Browser storage key	What it holds
steampressclear.v1	Which chapters you have opened, your best quiz scores, and sound on or off.

Exactly what each one sees is at glassbox.how/privacy.

Licences

• Code: MIT. Use it, change it, ship it.
• Explanations, text, images and videos (glassbox.json, glassbox/): CC BY 4.0. Credit “Glassbox, glassbox.how/e/steampressclear”.
• Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
• The Glassbox name and logo aren't covered by either licence. See the terms.

Found a mistake? Open an issue. Corrections happen in public.

Run it

It's plain HTML, CSS and JavaScript. No build step and no dependencies. Run locally, it contacts no other website.

python3 -m http.server 8000

Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.

Then open http://localhost:8000.

How it's built

File	What
index.html, css/app.css	The page and its styles
js/app.js, js/stage.js, js/ui.js, js/kit.js	The shared Glassbox 3D engine: chapters, 3D stage, controls, quiz, video director
js/press.js	Shared physics and models: steam tables, the iron's heat budget and thermostat, the bimetal strip, fabrics, the boiler press, the charcoal iron, chart boards and the 3D iron, press and box iron
js/chapters/*.js	One file per chapter: the 3D model, controls, text, key terms, quiz and video scenes
glassbox.json	Title, question, explainer beats, key terms, browser storage and credits shown on glassbox.how
reel in each chapter	The storyboard the Glassbox studio records into short videos
glassbox/	The published video, slides, thumbnail and post copy
fonts/, vendor/three/	Self-hosted Geist and Instrument Serif (SIL OFL 1.1) and three.js (MIT)