There's a persistent piece of trivia that old windows are thicker at the bottom because glass slowly flows downward over centuries, like an extremely patient liquid. It's a wonderful story, and it's wrong, but working out exactly why it's wrong opens up one of the more genuinely strange materials in everyday life. This episode looks at what actually makes glass different from ordinary crystalline solids, how it's made, why it's transparent, how toughened and laminated glass are engineered to fail safely, and how ultra-pure glass fibres ended up carrying the modern internet.

You'll come away understanding the real difference between amorphous and crystalline solids, why the old-glass-flows myth persists despite being false, how sand becomes a window, why glass lets light through at all, what makes toughened glass shatter the way it does, and ...