CoachStuffs differ wildly in how fast they let heat flow through them. A heat conductor is a fast lane — metals above all. A heat insulator is a slow lane: wood, wool, plastic, feathers — and the champion, still air, trapped so it cannot swirl. (The words are borrowed on purpose from electricity’s conductors and insulators; the two properties often, but not always, go together.)
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Example 34.5 (The slide mystery, solved)
The metal slide and the wooden bench spent the night at the same chilly temperature — the thermometer swore it long ago. Touch them: your hand is warmer than both, so heat flows from you into each. But the metal is a fast lane — it whisks your heat away in a rush, and that rush is what “icy” feels like. The wood takes your heat only in a trickle: barely cool. Your skin was never measuring temperature — it measures the speed of its own heat loss. Case closed, after four years.