Does filament moisture matter as much as relative humidity?  

RE: Does filament moisture matter as much as relative humidity?

Here is my experience on this topic:

Generally its held that a dry cabinet having very low RH inside will not dry out existing damp filament, and my experience agrees with that.
But I have seen discussions saying there is some evidence to indicate that storing damp filament in dry container can remove some moisture, just not all of it.

All that I can say on this is that my experience shows that if you take out your filament and use it on the printer for an extended period (10 hours +) in high (80%) RH conditions it can become damp and strings starts to show on the print, especially filaments like TPU.  If you then put those filaments back into dry storage they will not improve much, if at all. They need to be heated up to drive out the moisture that lies within the pores in the filament.

Currently, I feel the need to put every filament into the dryer after a print, which isn't easy or convenient if you have the MMU, there are 5 rolls to dry and only a 2 roll Eibos dryer to dry them in.  I'd get another dryer, but space is a consideration.

RE: Does filament moisture matter as much as relative humidity?

Professional Dry Cabinets absolutely work.  I have two E-Dry Ultra Low Humidity Cabinets that store some 80 rolls of filament.  I've even taken the time over a period of months of measuring the weight loss over various filament types.  It works.  Full Stop.  The downside is that they are not quick at drying already wet filament and they are very expensive.  Even my ePA-CF prints beautifully.  I also had mine fitted with ports so you can print directly from them... but I prefer to use my cheap Sunbeam Dyhradrator that holds 5 spools and which sites besides my MK3 (about the same size) while printing and then put the the rolls back in the Cabinet for storage. 

I'm less convinced on a plastic box with some desiccant.  

RE: Does filament moisture matter as much as relative humidity?

They do work, and it does not need to be an Ultra Low type.  I use one cabinet that goes to 26% humidity.  I also use a 10% humidity cabinet and for most filament the Ultra Low is overkill.  

Posted by: @bryn51

Here is my experience on this topic:

Generally its held that a dry cabinet having very low RH inside will not dry out existing damp filament, and my experience agrees with that.
But I have seen discussions saying there is some evidence to indicate that storing damp filament in dry container can remove some moisture, just not all of it.

All that I can say on this is that my experience shows that if you take out your filament and use it on the printer for an extended period (10 hours +) in high (80%) RH conditions it can become damp and strings starts to show on the print, especially filaments like TPU.  If you then put those filaments back into dry storage they will not improve much, if at all. They need to be heated up to drive out the moisture that lies within the pores in the filament.

Currently, I feel the need to put every filament into the dryer after a print, which isn't easy or convenient if you have the MMU, there are 5 rolls to dry and only a 2 roll Eibos dryer to dry them in.  I'd get another dryer, but space is a consideration.

RE: Does filament moisture matter as much as relative humidity?

I totally agree that professional dry cabinets having molecular sieve dessicant, automated dessicant regeneration work very well. But it depends on your expectations. I confess not to have tested efficacy on drying damp filaments by measuring weight. Only by observing print quality. My expectation is that at a minimum I require dry filament to remain dry inside, and that it does.

Mine is made by DR Storage in Taiwan with a capacity of  over 40 rolls. It has a very small footprint, good in my confined work room. It’s expensive by local standards but not as expensive as my printer, for example.

But, when I bought it I did not get them to include filament rollers or exit holes, so when I take out the rolls in 80% RH conditions they immediately begin to adsorb moisture, no matter what type of filament. I use PLA, PETG and TPU.

I agree on the plastic box dry storage. Silica gel desiccant just doesn’t cut the mustard. (I can sell you a couple of Kg real cheap if you want some.)   I think people lean towards low cost whilst ignoring effectiveness. Ignorance is bliss I guess. I try to promote molecular sieve when there is an opportunity. But often $$ wins over rationality. 

Regarding dryers. Food type dehydrators are not easily found where I live(Taiwan) and would be imported and not cheap. OK in US where food drying was once a fad. Common filament  dryers such as Sunlu and Eibos are competitive in Tw so that’s what I have. I ground my teeth and bought one in from China (grrr…)

RE: Does filament moisture matter as much as relative humidity?

The missing link in all of this is the fact there is no device (that I am aware of) readily available, reliable and cheap that can directly measure filament moisture content.

canvassing how it might work : 

a) by directly measuring conductivity. Confounded by not knowing baseline conductivity of the filament polymer.

b) by measuring density. You would need to cut a benchmark length of filament and measure its weight. A very delicate measurement due to the lightweight nature of filaments. And then compare it to a benchmark of dry filament.

so, it’s difficult but not impossible with (b) being the winner.

But measurement of a whole roll of filament is fraught with imponderables such as (not) knowing the exact length of filament on the roll. And you might have used some of it….

RE: Does filament moisture matter as much as relative humidity?

Just for giggles, I tried 'a' above.  There was a piece of PLA filament lying in the corner of the office, a color I have not printed for months, so I know it's good and damp.

My bench multimeter is a Vici, not laboratory grade, but more than adequate for experimenting and troubleshooting, and I know that on the ohms scale it's reasonably accurate to several tens of megohms.  I have no clue what the actual max resistance value of it is, and I'm too lazy to consult TFM (or even hunt for and find TFM).  I sanity checked it by measuring the resistance between my fingers and then tried to measure the resistance (hence conductance) of a length of known-damp filament.

Using EZ-hooks and placing them as close to each other as I can get, which is a fraction of a millimeter, I still get infinity.  LOL, what I expected, actually.  😉

I googled the resistivity of PLA and it appears to be well up there in the range of 10 ** 16 ohm-meters (peta-ohm range) which I also expected.

Yes, I would probably be possible to devise something to measure the resistance/conductance of a length of filament, but it would have to be a number of orders of magnitude more sensitive than what I have readily available.

Another thing to consider is what's in the filament other than plastic.  My instinct says that something like carbon black, a common pigment, or zinc oxide, a common white pigment, would be very significant in increasing the conductance of a length of filament.  More so with the common metallic pigments.

Now as for 'b' above, I don't have a lab balance, but someone who does might perform a quickie experiment, as in measure the mass of a known-damp spool, then dry it overnight in an oven/Ninja Cooker/commercial filament dryer/dehydrator/whatever and compare the dry mass to the damp mass.

As for what I will do, I'll probably continue just overnight drying suspected-damp spools of filament, as experience shows that the process works very well.

RE:

There is a long threat about all of this a couple of years ago - https://forum.prusa3d.com/forum/postid/189145/

This shows my results of first saturating then dry different filaments using various methods, the effectiveness and the time taken till no more weight was lost.  

RE: Does filament moisture matter as much as relative humidity?

I used a different measurement, and that is print quality.  I do not care how much filament weighs.  

Posted by: @jmone

There is a long threat about all of this a couple of years ago - https://forum.prusa3d.com/forum/postid/189145/

This shows my results of first saturating then dry different filaments using various methods, the effectiveness and the time taken till no more weight was lost.  

RE: Does filament moisture matter as much as relative humidity?

That looks like you really got into it in a scientific manner. Thanks to impressive, and informs current discussion. I’ll study it tomorrow since it’s late. 

RE: Does filament moisture matter as much as relative humidity?

Well it’s another thing - to assess print quality vs moisture content. I for one would like to know that. Since when quality deteriorates many just throw it in the dryer. But for how long. Looks like standard accepted times might not be enough in some cases.

a day or two ago I dried 2 rolls of TPU fiksmrnt for 4 hours. Then put one of them onto the printer and started using it. It was stringy as all s$&t. Temps on the print were already low to try to minimise stringing, and retraction also set high. 
I have not yet figured it out….

RE: Does filament moisture matter as much as relative humidity?

I put it in there for 3-7 days.  3-4 appears to be my sweet spot.  

Posted by: @bryn51

Well it’s another thing - to assess print quality vs moisture content. I for one would like to know that. Since when quality deteriorates many just throw it in the dryer. But for how long. Looks like standard accepted times might not be enough in some cases.

a day or two ago I dried 2 rolls of TPU fiksmrnt for 4 hours. Then put one of them onto the printer and started using it. It was stringy as all s$&t. Temps on the print were already low to try to minimise stringing, and retraction also set high. 
I have not yet figured it out….

RE: Does filament moisture matter as much as relative humidity?

The brand/quality of the product also plays a part in how well they print.  

Posted by: @bryn51

Well it’s another thing - to assess print quality vs moisture content. I for one would like to know that. Since when quality deteriorates many just throw it in the dryer. But for how long. Looks like standard accepted times might not be enough in some cases.

a day or two ago I dried 2 rolls of TPU fiksmrnt for 4 hours. Then put one of them onto the printer and started using it. It was stringy as all s$&t. Temps on the print were already low to try to minimise stringing, and retraction also set high. 
I have not yet figured it out….

RE: Does filament moisture matter as much as relative humidity?

Yes, it does. But my earlier post was about Filamentum flex 98A, not some Chinese cheaply from Amazon.

but, on my MMU I identified eSun PLA + as a likely candidate for the c$&@p filament award. It failed to respond to slicer params expressly designed to limit filament-end strings, when two other filament brands responded.

So yeah I’m across that issue. But it’s a roulette wheel putting filament of unknown dampness onto the printer, especially with the MMU, itself problematic.

RE: Does filament moisture matter as much as relative humidity?

Wow. You’re not a famed member for no reason !!! 
I am impressed how you mobilised into action so quickly, since I procrastinate …

but it seems like that question is settled, you nailed it! Well done !

 Thanks 

RE:

yeah... I got two spools from Eryone that was damp. I could hear it hiss and there was stringing. One was a gray spool of PLA and one a black color. Dried the gray one out as it was worse in stringing and it printed much better. So some are coming damp. At one time I thought the moisture might be penetrating the plastic, but if air can't get in, water molecules are larger. I smile when one mentions 30% humidity being a problem. My house has not been below 65% for 2 months, and at least 1/2 of the days have outside humidity in the 90's. Everything I print is from a dessicant sealed box. I have 10 of them.. A pain drying dessicant.  On a side not, I cannot view any of the graphs in this thread.. using MacOS & Safari. 

RE: Does filament moisture matter as much as relative humidity?

Humidity of air is a factor of temperature. 80% relative humidity at 15 degrees Celsius, is the same as 40% relative humidity at 30  degrees Celsius. They are inversely proportional.

If you were to suddenly cool down a roll of filament that had a moisture content of 80% relative humidity at 30 degrees Celsius to 15 degrees Celsius, beads of moisture would form on the filament, since 80% relative humidity at 30 degrees Celsius would be 160% relative humidity at 15 degrees Celsius.