ELI5 Cotton - why are line-dried shirts so stiff?

Why are clothes that are hung to dry crunchy/stiffer than clothes dried in a dryer? How does spandex make cotton stretchy? What does it mean when they say cotton 50% and something else 50% like polyester or lycra? Please explain bed sheets and thread counts?   ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: ldi1, prionbacon, dbmaniac, shoziku, aktuarie, motomike256, dansworth, quantumhamster, demanbmore, kstakka, platanosinpantalon, jarjarawakens and pescodar189. To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]