Thermal Conductivity

[Please note first] This app measures nothing. It has no sensor and no camera. You type in a thermal conductivity you already know, and it lines that figure up against fourteen everyday materials. It is not a tool for designing insulation. ────────── ≫ Thermal Conductivity — how fast does heat travel? Being a metal is not the point. Copper carries heat about five times as fast as iron, and metals differ enormously among themselves. Silver runs over ten thousand times as fast as air. Enter one figure and compare it against fourteen materials, from air at the quiet end of the scale to silver at the other. ■ How it works Type a number and the materials nearest to it line up. The ratio to your own figure appears on the same row, so you can see at a glance how far apart two materials are. Tap any row in the full scale to load its figure. ■ The fourteen materials Silver 429, copper 398, gold 317, aluminium 237, brass 106, iron 80.3, stainless steel 16.7, concrete 1.6, glass 1, water 0.6, wood 0.12, glass wool 0.04, polystyrene foam 0.034 and air 0.0257. Every figure is in W/(m·K), for around 20 °C. ■ Metals are not one thing Copper carries heat about five times as fast as iron. Set copper against stainless steel and the two are an order of magnitude apart. That is why copper and aluminium turn up in the base of a good pan: the heat spreads evenly instead of pooling over the flame. ■ What insulates is the air Polystyrene foam and glass wool both sit very close to still air on this scale. The material is not stopping the heat by itself; it works by holding air in cells small enough that the air cannot move. Crush it or soak it, and it stops working so well. ■ Water carries heat more than twenty times as readily as air That is why you feel cold the moment you are wet: the air against your skin has been replaced by water. A quilt or a coat works on the air it holds, and only while it is dry. ■ Fixed figures, and figures that vary Seven of the fourteen entries carry a range. Alloys vary with their mix, wood with its species and insulation with its density, so there is no single figure to give. The range is shown only for reading; every comparison is worked from the one typical figure. ■ Good for ▪ Putting the difference between two materials into numbers ▪ Finding out what "conducts well" actually means ▪ Explaining to a child how heat travels ▪ Any moment you see a figure and wonder whether it is a large one ■ Things worth knowing (included in the app) ▪ The larger the figure, the faster heat travels. The unit is W/(m·K) ▪ Copper carries heat about five times as fast as iron ▪ Insulation sits close to still air: what works is the trapped air ▪ Water carries heat more than twenty times as readily as air ▪ A row with a range has no single fixed value, and it is not a margin of error ■ How the app is built ▪ A single screen. No settings page, no tabs to hunt through ▪ Your last five entries are kept and can be tapped to restore ▪ Japanese and English, following your device language ▪ No account needed. The comparison runs on your device and your figures are never sent anywhere ────────── Note: every figure is a typical guide for around 20 °C. Alloys vary with their mix, wood with its species and insulation with its density. A row with a range has no single fixed value, and the range is not a margin of error. This app measures nothing, and it is not a tool for designing insulation.