Space is really cold, just over 2.75K, a whisker above absolute zero. Things contract when they get cold and expand when they get hot. Re-entry causes friction between the space shuttle orbiter and the atmosphere and friction produces heat – rather a lot of it. Also, we need to keep the weight down as much as possible. So, what can we do to protect the shuttle? Aluminium is light but can’t handle temperatures above 175°C, so it really needs some heavy-duty protection.
Much of the shuttle is covered with silica tiles made from essentially very pure quartz sand. The insulation prevents heat transfer to the underlying orbiter’s aluminium skin and structure. These tiles are such poor heat conductors that you can hold one while it is still red hot. There are about 24,300 tiles individually fitted on the vehicle, so the orbiter has been called “the flying brickyard”.
Unlike roof tiles, these tiles aren’t mechanically fastened to the vehicle, but they are glued. The tiles are brittle which means they tend to snap rather than bend and can’t flex with the underlying vehicle skin, so they are glued to felt Strain Isolation Pads (SIPs) with RTV silicone adhesive, which are in turn glued to the orbiter skin. These isolate the tiles from the orbiter’s structural deflections and expansions. Most of the tile is actually empty space which helps because air and a vacuum are very poor conductors. They’re also reusable so every time the orbiter comes down, it gets a new winter coat
The picture shows a white hot 1260 °C silica tile material being safely hand held 10 seconds after removal from a high temperature oven.