system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do towels and wash-cloths lose the ability to absorb water over time?

There are a few ELI5’s about new towels needing to be washed a few times before they become absorbent. I’ve observed the opposite too - my old dish towels and other cloths just don’t soak up water very well over time.
gpt
The ability to absorb water is that, when it touches water, the tiny water molecules get scooped into air pockets between the fibers of the towel. 

However, it's not picking up only water. It's also picking up whatever is in the water. This could be dirt, soap, hair, dust, etc. 

When the towel dries, the water evaporates, but the non-water stuff doesn't. Over time, these pieces stay clogged in the fibers and build up. The more stuff is clogged in the fibers, the less water it can absorb. 

Also just wear and tear. If you scrub the towel against a surface, the fibers will come off. They'll also come off from being cleaned. Less fibers means less scoops to catch water, so it absorbs less.