A lot of 3d printer filament is what's called "hygroscopic", meaning it absorbs moisture from the air. This will affect the filament diameter and reduce the appearance and strength of your printed part.
Filament Storage Blanket Advice
It's important to take your environment/climate into consideration. I see a lot of people on 3d printing forums saying moisture doesn't affect filament because "I leave mine out all the time, no problems". It's true that if you live in Nevada, USA where the average humidity is 30% then moisture probably isn't a problem. However, I live in Georgia, USA where the average humidity is around 70%. Therefore, a filament storage solution that resists moisture is an absolute necessity.
Effects of "wet" Filament
During printing, as the filament is extruded through the hot end, the moisture will rapidly evaporate. If you hear your hot end hissing and popping as you print, it is likely your filament has absorbed moisture. This leads to voids and defects in your printed part. I have often seen people spend countless hours troubleshooting their extruder and hotend due to reduced print quality while the problem was the filament, not their printer.
Filament Storage Solutions
Keep filament in the original package until you’re ready to use it.
Most filament manufacturers vacuum seal their filament with a desiccant package to protect against moisture.
Vacuum storage bags + desiccant packs
These work pretty well for filament storage. Make sure to get the kind that you can use a vacuum cleaner or hand pump to suck the air out and not the “travel” kind that you roll up. Be sure to use desiccant packs and be careful around sharp objects.
Gasketed Storage Bins (See Image) + DampRid
These are more durable and convenient than the bags. However, there’s no way to suck out air to minimize moisture trapped inside. Plus, you'll likely be reintroducing a large about of moisture every time you open the lid. As such, silica gel desiccants can't really keep up. Because of this, I recommend DampRid. You can buy it in a ready to use container or in bags to refill those containers. It's cheap and effective.
I’m not adding a link to the storage bins. Every time I’ve ordered one and had it shipped to me, it arrived broken. You’re better off going to a local store and picking them up.
Filament Drybox (my own design)
I designed and built a filament storage box with integrated filament rollers. As you can see, the tubing guides the filament from the box to my extruder. You can see the details of the build here.
For desiccant, indicating desiccant packs are good. However, once the desiccant in the packs is saturated you have to dry them out in an oven which is kind of a pain. This is why I like the EvaDry unit. It has a heating element built-in so to "recharge", you simply plug the unit into a wall outlet for a few hours.