All 3D printing filaments are hygroscopic which means that the material is good at absorbing water.
Its basically impossible to tell if a spool of filament is wet just by looking at it.
Wet filament becomes a lot more obvious, however, when you give a shot to print with it.
The biggest give-away is if you could hear popping and cracking sounds when extruding.
If you experience any of those issues, then a wet filament may be to blame.
Its possible to buy or make a specialised filament dryer.
Its also possible to use an oven or a food dehydrator to dry filaments.
Its also possible to make your own safe storage solutions.
In terms of desiccants, pretty much any should work.
Most desiccants can even be recharged when they become saturated by heating them up a bit.
