I’m only just moving into using petg, and finding mixed results. I suspect I’m not drying my petg spools often enough.
I’m curious if, after drying petg in a filament dryer (65C for 6 hrs, I understand), does it again need to be dried after a couple of days sitting in the AMS loaded with dessicant?
From what I have read on the forum, it sounds like the Bambu PETG-HF filament likes to absorb water from the air. Also sounds like it would need regular drying, like any other isotropic filaments.
If it’s in the AMS then that should lengthen the time in-between drying.
The above is only my opinion, from what I have read here. I use Overture PETG and have only dried it once I have taken it from the package. Never needed to dry it again.
All PETG love getting wetter, most filament is hygroscopic so will eventually absorb moisture from the air at different rates depending on type. I dry all my filaments the day the get delivered, I weigh the spools first then put them in a dehumidifier for 6 hours and check the weight again, pop them back in for another couple of hours and check the weight again. If they have stopped losing weight then I will take them out and vacuum bag them with desiccant for storage.
When I print they are in creality space pi set to the correct temperature for the filament, then when I finish printing I store them back in a vacuum bag with desiccant. I will re dry them if I spot a drop in printing quality using the same process again but check the weight every hour as they won’t usually take long.
Location dependent, PETG is fickle when moist so starting with a good base is key in my arrangement. I dry mine at delivery, then store in food cryo bags with a small desiccant wedge. Usually never have issue after that as I rarely leave them out for any period of time. Again its up to the individual and their environment, but at a basic level once at the start and monitor for defects if you’re leaving the spools out for a day, after that it’d prob be best practice to dry before storage again. Materials like nylon and tpu require almost surgical level treatment in my experience, they get dried before every use as a rule.
Edit to add, just read your other post and think your case needs a more intense dry, weighing to determine when to stop. Some dryers also aren’t as efficient and need to have the lid propped to evacuate the humidity.
Don’t let what you read in these forums force you to overthink things. Time is not the issue, moisture content should be your sole and only measure of the need to dry. So how does one measure moisture content? Here are a couple of techniques that are scientific in their approach.
Examples of putting this into practice
Short term Storage
Longer Term Storage
If you are able to suspect this, you’re not drying your spools often enough.
It’s not a “one a done” kind of thing. The plastic is constantly soaking up moisture from the air. Dry your filament every time you take it out of storage for a new print job.
Some plastics are more “hydrophilic” (water loving) than others. PLA doesn’t absorb a lot, but it gets brittle when it has. ABS, PETG, Nylon are all much more hydrophilic. I think Nylon can absorb close to 10% of its weight in water. These plastics don’t get brittle, but when the moisture hits the hot end, it turns to steam and screws up the extrusion.
6 hours is not enough time, IMO. Go for 24 hours if you want to be really sure. Plastic is a good thermal insulator, it takes time to get it hot and then it takes time for the moisture to diffuse out of the hot plastic. It’s not the kind of thing you can rush…
How often you dry isn’t the right metric. And drying after sitting in the AMS is a maybe/maybe not kind of thing.
The poly container Olias showed with a hygrometer and a bag of good/dry desiccant is a great way to store filament once dry. In storage in non-permeable containers, filament is kind of in hibernation of sorts and the hygrometer will tell you how it’s doing.
As to the AMS, that desiccant is expensive so you want rolls dry before going in and to keep the desiccant dry and active. I don’t know the translation between AMS humidity values and RH% but am adding desiccant bins with hygrometers to my AMS and will know then. But if high humidity in the AMS, maybe?
Very important to remember that wet desiccant can be a water source and actually humidify filament. Desiccants are used in museums and archival storage to supply water to items being preserved. They humidify the desiccant to the humidity they want in whatever container and drop it in. It either gives up water or absorbs it to hold humidity close to where they want it. You want to keep your desiccant “dry” for it to do its work since with filament we want it to always be removing water.
@Olias – great storage bins. Could you please say more about your short-term storage?
There really isn’t much to add about the solution that I’ve been using that hasn’t been shared on this rather long thread posted here.
If you’re curious as to what was in the photo, it merely came from this Printables profile but there are many others that are similarly designed.
https://www.printables.com/model/742565-wildone-drill-less-drybox-cap-with-hygrometer-and-/files
I used that one because it included STEP files, which makes it easy to modify. I modified the model to fit a PTFE fitting and added a stub with a 1.75mm hole as a filament anchor during storage.
I generally have avoided cereal box designs due to poor value and space inefficiency. They only fit narrow spools, Bambu spools as an example, are too large. Despite buying two sets on sale for under $4 each, I would have regretted paying full price. They clutter my shelf, and after adding parts for a “live feeder” brings the total cost to over $8 per box—bringing the total cost near the cost of 8 spools of PLA at the prices I pay. A purpose-built dryer was a more sensible solution to me at under $60.
While some swear by these dry boxes, they don’t make sense to me if one has a single printer setup. A member recommended a better bulk spool storage solution in the link above which drove cost down to under $3/spool, which I purchased at a local Home Depot. I’m careful with over-spending on every cool gadget I see since this hobby spending can quickly get out of control and I’ve found that many of the things I printed/designed/downloaded, didn’t get nearly the use I thought they would.
@Olias — I’m glad learn more about using a scale to manage moisture in filament spools.
Weighing a new spool and tracking weight loss until it levels off to determine dryness seems straightforward.
My challenge is that my spools seem to absorb a lot of moisture in the AMS, even though they contain plenty of dessicant, and I’m unsure when the spools need redrying.
Is the best approach to track the weight of all printed material and add that to the current spool weight to estimate moisture absorption? This seems like it would require precise tracking, and I’m not sure if it would be accurate enough to effectively monitor moisture content.
Also, that’s a really low price for PLA. Could you share your source?
There’s no mystery to my source. It’s Amazon. I’ve got a number of posts on here about that. When I first got my P1P I was paying >$25 and for Bambu >$28. Bambu went out of stock on black PLA for weeks and I needed to print an enclosure. So I was forced onto the open market and guess what? It’s a better world outside of Bambu’s ecosystem if you’re not an AMS user. Ever since then and with Amazon’s generous free returns, free freight for Prime users, finding cheaper solutions has become almost a second hobby like a competitive sport almost. 
On the subject of moisture monitoring. If you just abide by the practice of keeping on moisture card in your AMS, you will have a better ideas as to what the accumulated moisture is. Also, you’ve discovered the value of weighing your filament but did you know that the same is true for desiccant? One of the things I like about desiccant bags is that they come pre-measured. As an example, Wisedry and similar 50g bags are perfect for this purpose. You know how much they weigh and if the moisture card shows exposure, place both the moisture card and the desiccant bag in your favorite drying method and both get recharged. Then weigh it after drying to ensure that moisture has been removed.
So many people on these forums shoot from the hip, taking everything they see or hear as gospel, and worse, they perpetuate misinformation without verifying if it was true in the first place. In my commercial life, I’ve been burned too many times not to know that one should Always Be Questioning (ABQ). However, there’s no substitute for using the scientific method and verifying things for yourself—if for no other reason than to maintain your own sanity when mysteries arise.
Try this experiment: Take a plastic food container large enough to hold an open container of water. Pour in a measured amount of water, place a desiccant bag or measured bulk desiccant and a moisture card in the container, then seal it. Wait to see how long it takes for both to change color. I got results in as little as 12 hours, depending on the ambient temperature. To speed up the process, place it in a warmer area—a sunny windowsill works well.
Next, weigh the desiccant bag after a period of time and note the weight. Leave it in until it reaches its max weight from water absorption. Then, dry the desiccant and repeat the measurements. Measure the remaining water in the container (1g = 1ml = 1cc) to account for water loss. For extra precision, seal in a hygrometer for instant readings.
The experiment can be completed within 24 hours, but I extended it for weeks to ensure results leveled off. I repeated the experiment with consistent results using Wisedry Silica Gel desiccants:
Bambulab PETG filament spools: Before every use if the drying was older than 5 days and after every first opening - I threw away the last rolls last december and it came out something like your shared link - maybe just bad luck.
PETG of Extrudr and Fromfutura fillament, I can’t remember when I dried a spool last time - I don’t have an original packaged spool that isn’t completely used up within 30 days - Maybe just luck.
