I have seen multiple post lately where people are having issues with vacuum bag filament storage. Some of them say it does not work. In response, I decided to provide a detailed description of how to use the bags in the way that works for me. I know they work because I have filament that has been sealed for several months and the bag is still sucked tight around the filament and into the area between the sided of the spool.
The reason that vacuum bags are good for filament storage is that they minimize the amount of air in the container with the filament. Air at a given temperature can only contain a certain amount of water vapor. The less air in the container with the filament, the less water from it can be absorbed by the filament. This is why a vacuum bag is better than just putting all your filament in a big plastic air tight container.
I use the Esun system which comes with reusable bags, color changing desiccant, a vacuum pump, and a bag closer tool.
To make vacuum bags work you need to
- make sure the seal is tight so that no more air gets in after the vacuum process
- remove as much air as possible, thus minimizing the amount of moisture sealed in with the filament
- add desiccant to trap any moisture in the air that remains in the bag. (This is really not that significant.)
Side note: if you are curious about how much moisture can be in the air, put an open container in the sun where the air is warm. Seal it and put it in the refrigerator. Because cold air cannot hold as much moisture as warm are you will see condensation form inside the container. (The amount of condensation will vary based on where you live. In the desert it might not be a dramatic amount.) This is also why a filament dryer that has a closed container with no fan will show relative humidity drop when the heater is turned on. If the dry is sealed then moisture cannot leave the container. Relative humidity is just the current amount of moisture in the air divided by how much the air could possibly hold at the current temperature.
Load the Bag
Put the filament in the bag and put the desiccant, if used, next to the filament and not in the center of the spool. (If the bag seals tightly against the outside of the spool the air in the center of the spool is in a separate sealed compartment from the filament.) [To remove even more air, you could print an airtight cylinder to put in the center of the spool to displace that air from the bag too.]]
Seal the Bag
Use the tool to seal the bag. You can use your fingers just like you would with any zip-loc bag if you like, but the tool makes it easier to seal and makes sure you get it all sealed.
- when sliding the tool, you will need to squeeze it. If you just slide it then the clip might not be springy enough to completely close the seal on the bag.
- When you put the tool on near one end you will have to hold the corner of the bag while sliding the tool. This means there is the possibility of having the corner you are holding not sealed completely. To make sure it is completely sealed, after using the tool left to right and letting it slide of the right side, put it back on and go right to left.
Remove the Air
You must put the bag on a flat hard surface to use the vacuum pump correctly. It is unintuitive, because it seems like the two layers of the bag will be pushed together and prevent the pump from working. However, the check valve (hole for the pump) has a ridged surface on the bag that allows air to be evacuated even when both sides of the bag are pressed together.
With the bag flat on a hard surface, just turn on the pump and push it down on the bag centered on the valve. Stop when you have as much air removed as you like.
The result should look something like this. Notice how the corner with the valve is sticking out and flat.
When you check later, if the bag is still pressed in on the filament then the seal is working. If the seal is leaking the bag will want to relax to a shape larger than the spool. If you do have a leak it might be that the zip-loc did not seal completely, or it could be that the valve is not sealed. You can just squeeze on the valve when done removing the air to check that is sealed well. If the valve is faulty, Esun provides extra valves in the kit.