In northern Minnesota the humidity can vary greatly. Last weekend it was 90+% outside. While indoors the air conditioning had the house around 50%. And by winter time, the outdoor humidity can be as low 20% and indoors depending on heat source, around 30% to 40%.

I finally broke down and bought a dedicated filament dryer, Sunlu S2, because my trusty old food dehydrator died the week before. I do dry PETG when it tells me to, and I always dry TPU. But never PLA.

Just for fun, after I was done drying and printing some PETG, I dropped a mostly used spool of Sunlu white PLA into the dryer, (first time ever for PLA). That spool has been laying around in the open for at least 6 months now. The humidistat on the dryer showed 30%. I let it dry down to 20% and ran a test cube. No difference in print quality that I can see.

Dallas, I’ve never had an issue. Houston, I got all kinds of zits and pilling and was thinking about getting or making a filament dryer before we moved. Both can be pretty humid, but the difference between 60% and 90% is significant.

Southern Norway is quite good for keeping stuff in the open.
Around 35% now, peaked at mid 50s in summer and much lower in winter.

Never really need to dry PLA/PETG, but TPU does need it.

I do run both AMS every once in a while, mostly to regenerate the silica tubs a bit.

I did have stringing on PETG once, but drying while printing was enough to solve it.

I just finished out some PLA spools I’ve had for a couple years now. They’ve sat in the open with no drying. Humidity sits in the mid 40s generally right now.

I have humidity sensors in both my dryboxes and outside.

Where I live humidity in summer is 40-60% and the dryboxes will max out at 40% if left untouched.

In winter it’s 20-30%.

Petg starts having issues at 30 and you can hear the water boiling at 40

@matlag My printers are in the basement. During the winter, it’s dry enough. During the summer, it measures at >80% humidity. I’ve got a dehumidifier but can only get it down to around 60%.

In this situation PETG can only sit out for maybe 3 days before it’s noticeably wet.

I’ve still never had a moisture problem with PLA. It tends to simply be an age thing. PLA gets brittle and snaps when under constant pressure, say where it loads into an extruder or AMS.

I live in a dry climate. I don’t bother with PLA, but I dry PETG. I printed some stuff from a roll of PETG that had been open longer than a year, and looking closely at the melted plastic coming out of the nozzle, there was noticeable bubbles and stringing during printing. Once dried, all went away. People who claim you don’t need to dry some filaments must not care much about quality.

Outside, it usually sits around 65-70% humidity, over 80% during the summer. Hong Kong is like that unfortunately. Dunno about the room my printer sits in though, I don’t have a hydrometer in there, but I imagine it’s a little bit lower (maybe 60%? 70% in warmer months?). I don’t dry my PLA though and I’ve mostly had good printing experiences.

Too damn high

I’m of the general opinion that the hullabaloo about drying filament is largely not warranted in most cases. PLA is just not very hygroscopic and can sit out for months without any issues. Even PETG I don’t have any issues with it sitting out. The room I print in sits at about 50% humidity most of the time.

I keep most of my filaments in a box with dessicant that I bake maybe once a year, but I’m not convinced it is really doing much. The only reason I have a drier is that I started printing occasionally with materials that are much more hygroscopic (e.g. TPU).

Right now, around 50% RH indoors. I leave my spools of PLA on the printer for months or even years, and I’ve never had any humidity issues. If I were to speculate, my guess would be differences in additives being the main reason that only some people need to dry their PLA filament.

25%. My dehumidifier doesn’t go lower than that.

I have about 50% humidity and don’t usually dry my filament and I start to have issues with the outer layer of the spool snapping repeatedly when feeding after a year or two of sitting out. I used to have a dryer for cases like this but it got left behind in a move so I currently try to only use my new spools until I can get another one because I don’t trust using the oven and using the heat bed is really slow.

I have a spool of PLA that’s been sitting out for a year in 30-80% humidity and it printed up just fine, I didn’t even dust it off.

Summer humidity averages 15%RH and winter humidity about 40-60%RH outside. Generally my indoor humidity runs between 30-40% @72F but I don’t do anything special to control it.

I store almost all my PLA and ABS in open racks and rarely have a quality issue (Bambu, Kingroon, and Sunlu brands). My engineering filaments (PC, PET, ASA, and especially TPU) I will dry before use in an AMS-HT and keep stored in sealed containers with dessicant just as a housekeeping necessity. Sometimes I leave them out and it’s fine, but they are $ enough that I take care of them to avoid scrapped prints.

If you can’t get RH lower than 35% after 48 hours you need to renew or exchange your dessicant. Drying works by heating air until it’s RH is extremely low which causes water to migrate out of the plastic into the air via vapor partial pressure, then it gets absorbed by the dessicant to be removed from the system. OR, some dryboxes (ams-ht) continuously exchange air from the outside, which is energy intensive but provides a continuous supply of hot, dry air to remove water from the system.

Dessicant can only achieve an RH equal to its own saturation, which increases with exposure time, so starting with very dry dessicant is a necessity.

Air exchange is less effective in very humid climates, since your heated RH% will be higher, so sealed drybox + dessicant is usually preferred there.

If you aren’t actually removing the water with dessicant or air exchange, it will just stay in your drybox and return to the same RH you started at once it cools down.