system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why Does the Texture of Paper Change After It Gets Wet and Dries

Most things get wet, dry, and look similar to how they started. With paper, it ends up having a different texture after it dries. Why?
gpt
Plant fibers swell when wet, and shrink when they dry, somewhat like sponges.  Among the last stages in making paper is rolling it between giant metal rollers, while it's still damp, but in the process of drying.  This pushes the fibers together, helping them interlock better so that it's stronger when it dries and shrinks down, and gives it that smooth texture.  When you get it wet again, those fibers swell back up again, and "unlock" from one another, like hair on a damp day.  When it dries back out, unless you roll it back flat while still damp, those fibers will stay unlocked and frizzy.  Paper that's gotten wet and dried again will also be less strong and easier to tear than paper straight out of the package.  

There's also various chemicals that are added to the pulp to help the fibers stick together and not be quite as absorbent as it would otherwise be, and when you get it wet, some of those chemicals are diluted or washed away.

You can think of it like having naturally wavy hair, and making paper is like washing your hair, ironing it flat, and filling it full of product to keep it that way.  All it takes is a good drenching, or even just a humid day, and your hair is back to being all crazy-wavy.