I use our LG convection oven. It is efficient, it is big and room for 8 spools of filament. I use the temperature and time as per the Bambulab printer’s drying utility menu.
The spools need to lie on a flat surface- or they can warp. A cookie sheet works fine.
Downside is I have to get permission from my dear wife and in the summer it adds to the AC load. In the winter it is virtually free energy since it keeps the kitchen warm.
I’m in the process of giving the bambulab filament dryer utility a try. I printed bambulab’s recommended filament spool enclosure and the test is underway as this very moment. I weighed the test spool before, and I’ll weigh it again after. For PETG, the utility seems to be recommending 80C for 12 hours (flipping it over at the halfway mark), so I accepted that as the default. Not many of the standalone filament dryers on the market can attain 80C. A lot of them claim to do 50C, but youtube testing shows they don’t even manage that. The more expensive ones claim to reach 65C or maybe 70C at best. The PrintDry Filament Dryer PRO3 alleges to go as high as 85C, but it’s $199, and I’ve not seen any others offer that much headroom.
Bambulab recommended printing the enclosure in a higher temperature filament, but I printed it in PETG, and so far (with the glass top of the X1C off) it seems to be holding up to the 80C temperature.
Edit: Well, using a temperature probe, I see that it isn’t getting above 110F inside the filament spool enclosure, so I’ll have to put on the glass lid and see if that makes enough of a difference. If not, I’ll either need to increase the heat, or else possibly put some insulation around the enclosure. Alternatively, I suspect taping over some of the holes will help get to a higher temperature inside the filamet spool enclosure…
Cosori food dehydrator. Take out the shelves and stack up the spools. Not sure it will handle all 4 at once, but I know it will do 3 1kg spools. Huge fan delivers excellent airflow.
Great for backpacking trips, too 
I thought about using a $99 convection oven:
Desiccant removes moisture well but not rapidly. Suggest you check the absorption rate against your air volume and your relative humidity and see how long it would take. You have to not only remove the moisture from the filament but from the ambient air as well. Not sure the math works out, but Intuitively seems like it would not.
That temperature setting is for the X1C bed temperature, which is quite a bit more than the temperature reached in the spool enclosure or the chamber. Bambu’s filament guide recommends drying PETG at 65°C for eight hours. a more reasonable temperature for the interior of a dedicated dryer, and one that is close to most manufacturer’s recommendations.
If a dedicated dryer can’t reach a high temperature, a lower temperature will work, it just takes longer.
I’m becoming doubtful that the bambulab spool enclosure will ever get to 65C. I put a temperature probe through one of the holes, into the interior of the spool enclosure, and it shows that the internal temperature climbs very slowly. After 2 hours, it’s now at 127F (53C):
It’s still rising, but it’s a very slow climb.
Edit: Well, it never got above 130F, even after taping over nearly all the holes in the enclosure.
The funny part is that it noticeably heated up the entire room that it was running in. I don’t think it will be receiving an energy star award this year…
What became clear when I went to flip over the spool of filament being dried at the 6 hour mark is that the bottom of the spool, because it was in direct contact with the X1C heated bed, was heated to 80C, even though the top of the spool never got above 54C (130F). Hence, it’s not so much heated air that’s doing the heavy lifting as much as it is just direct conduction from the heated bed. This does make it quite a bit different from all the purely heated-air designs that are on the market. I can see why flipping it over is essential to try to improve the drying uniformity.
In any case, the filament drying process is now done, and weighing the spool before and after, I see that it has lost 3.41g of weight. I presume most of that weight loss is water, though some of it might also be outgassing of chemicals from the filament, as the room has a kind of plastic smell to it now immediately following the procedure.
Well, then, how does it print? That’s what really matters, and I’ll be testing that next.
Edit: Yuck. It still prints poorly as compared to a fresh roll of filament from the same manufacturer. Maybe it was no good in the first place, or maybe it cannot be rescued. Or maybe this is not a good filament dryer.
Disappointed. 
This is how the old spool of sunlu PETG that was “dried” for 12 hours using the Bambulab dryer utility printed:
and this is how a fresh spool of sunlu PETG printed the same model, using the exact same slicer settings:
Why the difference?
For whatever reason, different colors of the same filament sometimes cannot be printed with the same settings. However, I’d suggest trying to use an actual filament dryer to rule out the possibility that the Bambu Lab “filament dryer” isn’t the cause.
I concur. I’m going to give this “FixDry” a try. It claims it can do 70C for up to 48 hours. I’ve loaded it in, and “we’ll see.”
The temperature seems to bounce between 62C and 69C.
That’s better than most inexpensive filament dryers.
Home Depot Husky box is connected to X1C with filament feed tube. Holds large and small spools.
Desiccant keeps box interior dry a very long time.
No need to remove filament when not in use.
If like me you ever wondered how the cheap, off-the-shelf filament dryers might work, well I got it it figured, having done some measurements on the one I got (above). Do they use PWM or a PID to keep the temperature on target? Heck, no! You’re obviously thinking too hard. Let’s strip it down to basics. First, there’s a fan, which runs continuously, regardless of whether or not it needs to. Second, there is a heating element blown over by the fan, to pump hot air into the enclosure and which turns on-or-off like your grandmother’s thermostat, but with far worse hysteresis. Yep, that about do it. 19th century design, built with the cheapest parts, but gussied up with an LED screen, because, you know, customers want technology. On average it burns about 40ish watts.
Reporting back: After 24 hours on the FixDry with a target temp of 70C (apparent heating range varied between 62C and 70C), I weighed the Sunlu gray PETG filament again and it had lost an additional 0.71g of mass. It seems we’ve reached diminishing returns, so I tried printing a benchy with it, and… no bueno: same type of problelms as before. Unuseable print. This Sunlu spool had been purchased in January, 2021. That was the beginning of the covid pandemic so–who knows?–maybe for whatever reason Sunlu simply shipped everything they had then in inventory without regard to quality control rather than carry the cost of goods on their books through Armageddon.
Anyway, enough already. I dumped the sunlu GRAY PETG in the trash and reached for an even older spool of Hatchbox Orange PETG, purchased in August 2018 and still in its original, factory sealed packaging. I loaded it on the X1C and printed a benchy. Result: vastly better than the Sunlu, but with some stringing. This seems like a better test sample for a filament dryer, so I’ll throw it on the FixDry for 24 hours and see if it makes any difference.
The stringing could maybe (?) be fixed just by slicer tweeks, but Tom Sanladerer says the first step is always to guarantee that your filament is dry before you attempt that, which is why I’m heading down this rabbit hole of trying to find a good filament dryer.
Follow-up: After 12 hours in the filament dryer set at 70C, 1.73g of mass was evaporated/boiled-off/outgassed. Here is the “before” measurement:
Bottom line: Unfortunately, there was no visible improvement in the printing of Benchy
Final attempt: I heated the same spool of hatchbox orange filament for another 10 hours, resulting in a loss of 0.65g of mass. This time I’m going to use the Bambulab PETG Basic filament profile instead of the Generc PETG profile. I’ll print another benchy using all default settings. I have a hunch that Bambulab may have tweaked the settings to work more favorably than the generic settings. Anyway, that’s the gamble. Now printing… We’ll just have to wait and see whether the gamble pays off. I mean, CNC Kitchen and Tom Sanladerer both claimed success in reviving even old spools of PETG, so what I’m doing “should” work, shouldn’t it?
I think so. The issue is more likely being caused by your slicer settings. The default Bambu Lab profile did not produce good results for me when printing Polymaker PolyMax PETG.
Reporting back: Good news! Switching to the bambulab PETG Basic profile was a vast improvement over the Generic PETG profile. On the left is the Generic, and on the right is the bambulab Basic PETG Profile:
Unfortunately, because I was on the verge of giving up, and this was a Hail Mary, I changed two variables at the same time on a best-guess basis: therefore, I don’t know how much of the print on the right is due to filament drying and how much is due to the change in PETG profile.
It’s still not perfect, but IMHO it’s already good enough for iterative design prints, where prints are quickly reviewed for fit or function or some such and then quickly discarded. I would probably use a freshly manufactured filament spool if I were doing a final print, as this rescued filament is not yet in the “it just works” category, whereas the fresh stuff is “fire and forget” without needing FAFO.
I tried reading every frikkin large test review to figure out what would be the best filament dryer that preferably would not cost the clothes from my back…
1/ Tried kitchen oven on recommended temp & procedures
Turns out the thermostat in the Cylinda my landlord provides is not that accurate, as in despite having a knob with different temperatures increasing it really has two temps - Nothing .vs Hell and it toggles these two to come to some sort of bad choice middle territory that absolutely melts anything you would put in your 3D printer…2/ Got a cheap convection oven of Amazon, unfortunately it seems to have used the same brand of thermostat ass the above Cylinda oven. At least another pair of full PetG rolls melted even worse that in my kitchen oven.
3/ Got a mushroom dryer that was good in size and they sold additional layer rings as to extend the housing and increase amount of mushrooms (filament) possible to dry.
Tried different setups/extensions/asf
NOTICE!!! This time, after 5kg PetG burnt worse than the scorched earth in the Mad Mex ripoffs, I put in started rolls and smaller cobwebs of PetG filaments various brands.
This I thought would actually work but then the dryer fan hit the… thermometer… just totally over the place, like nothing you even expect and still work.
Returned to… hmm was it Jula or Clas Ohlson?!? Anyways I still dunno if it was a monday dud or if it stank like a skunk in the electronic factory?
Right now I had been heavily invested in the top list/reviews/reddit discussions asf etc aso,
the money, time & petrol (I live in the desolate northern wilderness of Sweden so the distances are no picnic to say the least) the money I blew on the above ■■■■ would have purchased a twin set of the most expensive filament dryer in any review I laid my filament dryer hungry eyes on 
However I got effin annoyed, it is as said above really pricey and still they sell a lot of crepe you have to pick on the side and try and guess what you need and then they milk you like a cow in a free hentai comic online… sigh
Basically it seems to have a fan inside to drag the moisture out but it seems like… ANNOYING to use, and I will not use stuff that has too annoying procedures, just stay clear of stuff that just makes the air go out of me… (cept my boss of course)
So I purchased the top listed Sunlu S2…
And yes it is good, but to my surprise it had no fan inside or anything that would vent the moisture out of the dryer, I could literally see the moisture collecting inside the top of the plastic housing… oh no… is it one of these modding things!?!
I put a wedge in and run it like that, but it is far from optimal and now I constantly wonder how much more it would dry the filaments if it had a proper fan with ventilation?!?
This one has wonderful sets of rollers that makes the filament roll spin like a cat on catnip! Further it can stay on… possibly infinitely?!? I wanna print directly out of this one when I dont have to prioritize the AMS - since the AMS gets PMS with half of the eSun/Stronghold PetG filament rolls when you pop the string in the feeder hole it stops it cant push past the winded up rolls since theres not enough space… sigh… how ridicilously flawed on products otherwise so many lightyears ahead of all other competitors so it looks like pure sci/fi! How could they make it to tight to load standard rolls?!? (Yes thats a proper question, what happened here when everything else is so thought through?!? Makes me genuinely curious.)
So I looked up the top listed Eibos Cyclopes that has space for two rolls and A FAN BUILT IN!!!
Just arrived and when I looked at the unpack videos I just realize this one is the one that has the so called lethal flaw where it blows the hot air straight up in the arse of the rolls drying and melting them to plastic clumps in said same spot… arghhh…
I seen mods but there are like a bazillion, and all mods are listed with cons (post apocalyptic, I mean in after hand they where made people found flaws with the mods too) the heatshield mods appear to damage some other parts like overheating sides asf
The riser mods looks really varying in reviews, could you knowledged mates give me some guidance and recommendations for which riser is the best most proper?
Are you sure your Sunlu S2 doesn’t have a fan? The current model does. If you can still return yours then do that and get a new model one. You can hear the fan clearly so it should be obvious which you have…
