system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why towels and clothes get stiff when you dry them in the sun?
gpt
Domestic water is not usually pure water, it often contains salts and other minerals. As the clothes dry, these salts and minerals are left behind in the threads of the fabric forming crystals.

Air-drying is a relatively slow process and the clothes are mostly stationary, so these crystals can get bigger, making the fabric stiffer. However, it doesn't take much to break them so clothes feel much softer once worn.

Tumble dryers constantly tumble the clothes through the drying process, which keeps the minerals from forming crystals big enough to noticeably stiffen the clothes.