You mean these videos?
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Excellent, loved those, thanks!
If you watch them, itās actually the opposite, being in or out of the tubing had no effect.
What the video shows is actually a few interesting things that many of us observed already without ever paying too much attention.
Filament, especially PLA as it seems, has a pre-defined structure, be it crystalline of through the polymer chains.
Water free PLA would be brittle as glass without modifiers.
Once on the roll, the PLA is set in stone so to say, only the additives ensuring a proper shelf life while the vacuum sealed bag limits oxidation and degradation.
It is still not fully clear what exactly causes PLA to age and degrade so differently for so many users.
Only things we know for sure so far:
Oxygen over time has a bad effect on fresh filament but very little on printed parts.
UV light is very bad while temperatures above 24 to 26 degrees seem to cause the filament to age faster.
A long list of chemicals that either soften (dissolve) PLA or make it brittle by affecting the additives and polymer chains.
What it basically still unclear is how exactly any of this makes our filament go bad.
I know of no manufacturer that ever provided any long term study on their stored filaments under various storage conditions ā¦
Yes, it can get too dry and I do not believe its a moisture problem. I have stored some PLA in my dry cabinet that is under 5% humidity and PLA DOES get brittle. I think its just age.
I have a print that is really brittle using PLA. Every time I print it it breaks. It is small and really thin, it is a game token.
I am new to Bambu and 3d printing. How can I make it the print thicker?
I have 3 different ptfr tubes (from different sources). In one of those three, my filament goes ultra brittle in no time. It also kinda sticks in there a bit and does not glide through it perfectly. Its very annoying.
I assume that it is not actually teflon at all, and that it is somehow reacting to the pla?
Is the bad one straighter than the others? Or maybe does in bend in the opposite direction of the spool winding?
nope, just the same, also the filament breaks in the first millimeter into the tube, no brnt there at all. its like the pla reacts with it somehow.
I believe it might be dome cheap plastic pipe thats not teflon at all
Unless you are planning on using nitrogen purging it will be very difficult to get below and sustain <15% RH. The only systems where I have seen moisture levels consistently below 5% are really well sealed containers with active GN2 or dry compressed air purging.
I have consistently 0 ā¦ 3% RH in both my AMS1 and the filament bags, using molecular sieve 3A.
I assume you have very high confidence in the calibration of whichever device you are using to measure RH.
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Yes that is true 
As reference I use an SHT31 demoboard from Sensirion, a swiss company that is one of the most renowned companies for environmental sensors. The SHT31 has a specified tolerance of Ā±2% in the range 0ā¦99% and I think the manufacturer of the sensor did everything right in the demoboard. It is quite easy to mess it up in the PCB.
But the key really is the molecular sieve. It relentlessly draws humidity from air. Its most common use is in chemical industry for removing humidity from pure technical gases.
When I started with silica gel, humidity never dropped below 17ā¦20%. The molecular sieve is a completely different story. It has bunch of disadvantages, but opposed to silica gel, it takes up water even from very dry air.
This page has a nice graph that illustrates why RH can get so much lower with molecular sieves: Desiccant Charts - SorbentSystems.com
This is a repost of mine from another site:
Iāve heard all the reasons for PLA breaking inside PTFE tubeā¦ PLA is wet; PTFE is bending the PLA opposite itās resting state; Youāre using cheap PLA, etc. So I ran an experiment:
Dry PLA (fresh spool, in dry box at less than 30% RH); PTFE curved in same direction as spool; PTFE with 2mmID & 4mmID and both sealed at free end; new PTFE vs one that has been used to feed filament for couple years; Sunlu PLA+. One filament was inside a 1/8 copper tube, one was left in the open (NW Oregon, RH 40-80% over 30 days, no A/C). These were my controls. Filament was left in the tubes for 90 days, then checked. Results:
1-filament inside 2mm new PTFE tube broke with minimum traction, in multiple spots. I think it was broken spontaneously;
2-filament inside 4mm new PTFE tube broke with minimum traction.
3-filament inside 2mm old PTFE tube broke with minimum traction
4-filament inside copper tube was intact and flexible
5-filament left open was intact and flexible, but could not be bent double without breaking
My conclusion:
There is some kind of reaction between PTFE & PLA which results in the latter becoming severely brittle, much more so than due to humidity. The age of the PTFE has minimal or no effect. Whether the reaction takes place over distance, or only at contact points, I cannot say. I use PTFE to feed filament from dryer box to my printer, and the 2 PLA feeds are constantly broken when not actively used. The PETG and ASA feeds have no issues. Looking for an explanation from some chemistry guru out thereā¦
Think this was a thread I started, but this happened to me again with a generic PLA brand sitting in the tube for about a month. Spool was sitting on the back of the printer, uncovered.
The only part of the filament that was brittle was the portion inside the tube, like before. After trimming, the rest of the spool was fine and I successfully printed several jobs.
I donāt dry my PLA, never needed to. Partially used spools sit open. No problems printing.
K
It is a good exercise to read the forum posts for your hardware because that is the first place you are going to see a problem. Over time you will develop a sense of problem areas for the various printer models.
Here is a prime example. Does not happen every single day but does happen more than once a week and that is plugging in the 3 connectors on the P1 Series hotend. Does not take long to realize those tiny plugs are an issue.Tiny connectors, confined space, recipe for trouble.
The same can also be applied to something like your theory about PTFE+PLA= 
I have a P1S, 2 AMS, 1 AMS 2 Pro, 1 AMS HT. that means a lot of PTFE tubing and like many people, print a fair amount of PLA. I use BL filaments pretty much exclusively.
I have had my printer about 14 months now.
While Iām a believer in āNever say neverā, this is the first time I have heard anyone suggest there is a conflict in material properties between PTFE and PLA. in my 14 months of BL P1S ownership plus a year with an Ender3.
Ptfe tubing seems to be the standard carrier for filament across all the manufacturers as far as I know.
PLA use is also pretty pervasive throughout hobby level printing.
While anything is possible, I think incompatibility between PLA and PTFE is a very low probability problem. Your PLA getting brittle is a thing. Being caused by PTFEā¦?
YMMV
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Wow, great experiment with for me surprising results!
I can offer one more often heard explanation for brittle PLA: I heard that it is very susceptible to UV light. Were the PTFE tubes exposed to sunlight? If not, it is clearly the PTFE. if yes, it could have been both, the PTFE or UV.
For anyone who likes long (maybe boring/tedious) tech reads, here is the general wikipedia on PTFE
I did find a few things interesting, related to other posts related to maintenance, not this one:
Musical instruments
PTFE is often found in musical instrument lubrication products, most commonly valve oil.
Lubricants
PTFE is used in some aerosol lubricant sprays, including in micronized and polarized form. It is notable for its extremely low coefficient of friction, its hydrophobicity (which serves to inhibit rust), and for the dry film it forms after application, which allows it to resist collecting particles that might otherwise form an abrasive paste.[52] Brands include GT85, Tri-Flow and WD-40 Specialist
(Edit: This sentence removed by poster, who while finding it rather ammusing, realized there are certain issues involved with the statement)
As far as this thread and whether it maybe part of the issue with brittleness, it doesnāt sound like it, although PTFE can be very permeable to moisture in some circumstances (e.g. Gortex) so I guess itās possible that depending on the tube and itās environment it could possibly be creating a high moisture inside the tube (edit: or possibly even trapping moisture given off by the filament). Also unknown is the manufacturing of any specific tubing and what contaminants any individual manufacturer might be introducing.