If you've ever used a old wooden railway sleeper to form the edge of a flowerbed, you'll know that it's a lot of wood. Peter T has spotted this interesting news that railroad builders are turning increasingly to polyurethane (PU) sleepers or ties, because they have "better dimensional and weather stability than wood and are lighter than concrete." And so fewer forests will be chopped down to form railway tracks.
What happens when it gets really hot? Do they melt?