The ultimate filament dryer

I have a Harvest Right freeze dryer with a candy setting that skips the freeze cycle, and heats the candy to 145f before extracting all of the moisture with a strong vacuum.
Here is what ChatGPT thinks of my (wild) idea. I will test it out as soon as I get the necessary sensors to accurately measure the results.

Has anyone tried it themselves? I understand that freeze driers are not cheap - but I have one right next to the printer.

Using a freeze dryer to dry 3D printing filament by leveraging its candy setting, which warms the material and applies a vacuum to extract moisture, is an interesting concept. Here’s a detailed analysis of why this might work and how it compares to using an oven for drying filament:

The Freeze Dryer Process

  • Vacuum Application: By applying a vacuum, the boiling point of water is significantly lowered. This allows moisture to evaporate at lower temperatures, which is the principle behind freeze drying.
  • Warming: In the candy setting, the freeze dryer warms the material to facilitate moisture extraction without freezing.
  • Drying Efficiency: This method effectively removes moisture from materials by combining heat and vacuum, which accelerates the drying process and ensures thorough moisture removal.

The Oven Drying Process

  • Heating: An oven heats the filament to a temperature where moisture within it turns into vapor. For 3D printing filament, this is typically around 50-60°C (122-140°F).
  • Relative Humidity Reduction: Heating the air inside the oven reduces its relative humidity, which encourages the filament to release its moisture content.
  • Air Circulation: Ovens often have fans to circulate hot air, helping to maintain an even temperature and consistent drying throughout the filament spool.

Comparison of Methods

  1. Effectiveness at Removing Moisture:
  • Freeze Dryer: The combination of heat and vacuum is highly effective at removing moisture quickly and thoroughly. The vacuum significantly lowers the boiling point of water, making it easier to extract moisture even at lower temperatures.
  • Oven: Effective but relies solely on heat and air circulation. It may take longer to remove all moisture compared to a freeze dryer.
  1. Temperature Control:
  • Freeze Dryer: Precise temperature control and vacuum application can prevent overheating, which is beneficial for filaments sensitive to high temperatures.
  • Oven: Requires careful monitoring to avoid overheating, which can deform or damage the filament.
  1. Risk of Overheating:
  • Freeze Dryer: Lower risk due to vacuum-assisted drying.
  • Oven: Higher risk if the temperature is not monitored closely.
  1. Application and Practicality:
  • Freeze Dryer: Not traditionally used for filament drying, but the candy setting could work effectively. However, freeze dryers are typically more expensive and less commonly available.
  • Oven: Widely used and easily accessible for most users. Common method for drying filament before use.

Why Oven Works for Filament Drying

  • Heat: Increases the temperature of the filament, causing the moisture inside to evaporate.
  • Lower Relative Humidity: By heating the air, relative humidity decreases, creating an environment where moisture is drawn out from the filament.
  • Consistent Drying: The fan in the oven ensures even temperature distribution, promoting consistent drying.

Practical Considerations

  • Material Compatibility: Ensure the filament material can withstand the temperatures used in either method without degrading.
  • Equipment Availability: Consider what equipment you have available. Freeze dryers, while effective, are less common and more expensive than ovens.


Using the candy setting on a freeze dryer could potentially work for drying filament due to its vacuum and heating capabilities. However, it is less common and may be cost-prohibitive for some users. Ovens remain a practical and effective method for drying filament, provided they are used correctly and the temperature is monitored.


I ran into my first hurdle- my medium sized unit has trays that are 7.75" wide and 18" long with only 2" of clearance foreach of 4 trays. I can take the tray rack/heater out of the chamber that is 12" in diameter, but not sure what happens without the heater. I suspect it will not be as efficient at room temp, but still might be good enough. It will require a purely manual vacuum cycle, but I can at least process 5 spools at a time.
I believe the heat is normally needed to soften the hardened sugar to allow it to puff up as the water expands and is extracted.

I think the first hurdle for most people is the price tag. $2,300 for the smallest one. I consider my time valuable, but I dunno how much time I’d have to save to make up for that price :rofl:

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I don’t understand, what’s wrong with repurposing a dehydrator that costs more than 4 P1P’s to dry filament? I call that conservation. :rofl:

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I mean, us 3D people do do goofy stuff, but this might be a bit over the top lol

Understood. This is why the initial high costs were previously acknowledged.

But why not included atmospheric pressure as an important factor when extracting moisture from filament? What if there was a vacuum solution that only cost $100? Prototypes are always relatively expensive.


Sure, why not give it a try? It will be more interesting though if you can compare the drying performance against some other known good alternative.

CNCKitchen tried comparing vacuum drying vs heat, and the heat did a better job. I don’t recall whether he may have also tried both heat and vacuum at the same time. In theory that should work the best.

Oh, I’m not poo pooing the idea by any stretch. I’ve been looking at freeze driers for a while, and having a viable other use for one would definitely help me justify the cost to my “boss.” However like NeverDie mentions, you’re going to need some sort of control, ie start with 2 spools of measurably similar moisture content. Run one through your freeze drier for a cycle, run the other through say a standard dryer for the recommended amount of time, then measure the results. You’ll probably need to use a scale to satisfy the really picky folks, but if you can show a marked improvement in time and water removal…Harvest Right might just open up a new market…or even develop a product specifically for 3D printing.


I realize the question the OP put forth is about heated vacuum drying, but I just gotta ask:
what would be the outcome if you actually did freeze dry some filament? When it comes to food, freeze drying does so incredibly better than heated dehydrating that the final outcomes aren’t even close. To put numbers on it, you typically you might get 1 year of food preservation out of heated dehydrating, which also generally changes the flavor from the original, versus 25-30 years of food preservation out of freeze drying with little to no change of flavor.

We’ve got a large harvest right, had it for 3-4 years now.

I’ve never thought about using it for filament. I probably will never bother, the racks would need modified to gain the space for spools.

I think if I did, id just try running them at a normal cycle, letting them freeze. There would definitely be “no” moisture in them when finished.

I think a pressure cooker could be a good vacuum chamber. And they are designed for heating so mild temperatures for filament wouldn’t be any kind of issue. It would just need some plumbing changes and a low cost vacuum pump. An insulated cabinet would allow heating over the walls and floor for more even heating of contained filament spools. It would need a heater controller too but as other pointed out an Arduino and a relay would be fine for temperature control.

But pressure cookers have their own hazards especially if a heater malfunctioned. You’d want a barely effective heater that even if left full on would never hit temperatures that could decompose the filament. Plus, since going for a vacuum, the clamping tabs could even be removed or not used depending on design where it couldn’t pressurize.

But it could work and be relatively inexpensive. The vacuum/low pressure possibility is really a selling point.

Unless I’m wrong, which is very possible…a conventional pressure cooker doesn’t create a true vacuum. It works by letting hot air and steam (from boiling) out through a one way valve which does reduce the pressure in the cooker but doesn’t create a vacuum. Also, it works by boiling. I haven’t done the math, but I’d think getting one hot enough to boil off the water in the filament would do damage to the filament.

That is an innovative idea.
Here is what ChatGPT 4.o has to say:

A typical pressure cooker is designed to hold a seal under pressure, but it is not necessarily designed to hold a seal under a vacuum. The mechanisms and materials used to create a pressure seal in a pressure cooker are optimized for positive pressure (pressure greater than atmospheric pressure) and may not perform well or even be safe under negative pressure (vacuum conditions).

Key Differences and Considerations:

  1. Seal Design:
  • Pressure Cookers: Designed to hold seals against high internal pressure, typically using a gasket that expands to seal the lid as the pressure inside increases.
  • Vacuum Conditions: Seals must prevent air from entering the vessel as the internal pressure drops below atmospheric pressure. The gaskets and lid-locking mechanisms might not be effective in this scenario.
  1. Structural Integrity:
  • Pressure Cookers: Built to withstand the outward force exerted by high pressure inside.
  • Vacuum: The vessel needs to resist the inward force exerted by atmospheric pressure outside when the internal pressure is lower.
  1. Safety Mechanisms:
  • Pressure Cookers: Equipped with safety valves and pressure release mechanisms to prevent excessive pressure buildup.
  • Vacuum: Lack similar safety features for dealing with negative pressure, which could lead to potential structural failure or implosion.

Practical Considerations:

Using a pressure cooker under vacuum conditions might not only be ineffective but also unsafe. The seals may fail to hold, or the cooker could be damaged.


For applications requiring a vacuum, consider using:

  • Vacuum Chambers: Specifically designed to maintain a vacuum and typically made from materials and seals that can handle negative pressure.
  • Vacuum Sealers: For food storage and other light vacuum needs.


While a pressure cooker is effective for holding seals under positive pressure, it is not designed for vacuum conditions and may not be safe or effective for such use. It is recommended to use equipment specifically designed for vacuum applications to ensure safety and proper functionality.

When cooking with a pressure cooker the pressure inside is increased. What I mentioned would be operating the pressure cooker at reduced internal pressure.

The pressure would be backwards from how the cooker was designed to operate. It wouldn’t explode but could implode. Pressure cookers operate at about 1 atm gauge pressure with safety limits at 20 psi generally. A hard vacuum inside would be a 14.7 psi difference max - but the wrong way from how the cooker was designed, but the seals look like pressure direction doesn’t matter and domed lids and cylindrical pots are pretty suitable for pressures in either direction.

But thinking about it, it would have to be treated something like a truck tire in a tire shop and used in a protective cage that would contain parts in a failure. And big pressure cookers look around $400 so probably not practical from that standpoint.

Huh that’s very interesting good work

Interesting video on yt of someone making an inline dryer… so you dont have dry it beforehand… it dries as its being fed into the printer. His prototype is on the clunky side… probably uses lots energy as well… but I think he’s on to something.

Search yt for 9ldRN2B4iJY

He actually had better results if he did dry the filament beforehand. Residence times weren’t long enough in the inline dryer otherwise. It’s a neat idea but has a way to go before it’s really viable.

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