Filament drying calculator

Why the right number depends on your dryer

A drying temperature is a window, not a single number. There is a floor, the temperature the filament needs to actually release its water, and there is a ceiling, the temperature where the spool softens or the plastic starts to degrade. Most charts give you the floor and ignore the ceiling, which is how people melt spools in a hot oven or ruin flexible filament in a dryer that runs too warm.

The ceiling matters more than it sounds. TPU is the trap: it wants roughly 55 to 70C to dry, but a soft TPU spool can start softening around 50C, so the number that dries it is the same number that can deform it. Nylon runs the other way, its published range is 70 to 110C and the cool end takes a day rather than an evening, so a 70C dryer is working at the bottom of its window. And the window is not only about the filament: Prusa ships spools rated anywhere from 45C (old cardboard cores) to 150C, and people have melted printed PLA spools at a 50C setting. This is why the tool asks what dryer and what spool you own instead of just handing you a temperature.

Lower temperature works, it just costs you hours

If your dryer sits at the cool end of the published range, you are not doing anything the manufacturers have not blessed. eSUN's own datasheets list 70C for both PC and nylon, and Spectrum publishes 60C for 12 hours on neat PA6, the lowest figure I found from anyone. Give a cool dryer more hours instead of more heat. One Australian retailer's support desk suggests doubling the time for every 5C you are under; treat that as a rule of thumb from a shop, not a law, and confirm by weight rather than the clock. I went looking for a minimum effective drying temperature across roughly two dozen filament brands. Nobody publishes one.

The real limit in a cool dryer is the air. Drying works by surrounding the filament with air dry enough to pull moisture out, and how dry that air gets depends on heating it and exchanging it. A hotter dryer collapses the air's humidity further, so it reaches a lower moisture floor and gets there much faster (a PA6 slab that needed a year to equilibrate at room temperature managed it in three weeks at 70C, in the one academic dataset that measured it). A cooler dryer with good airflow closes part of that gap, which is why Polymaker says outright that ventilation beats raw heat. The one tested failure is Fillamentum's: TPU 98A at 50C stayed wet after 24 hours. Everything else is slower, not impossible, and the weight check settles any argument.

How to actually tell it is dry

Weigh the spool on a cheap 0.1 gram scale before you start and again during drying. When the weight stops dropping, the filament has given up all the water it will at that temperature. That is the only home method that actually works across every material.

Two traps to skip. The dryer's own humidity readout hitting its lowest number does not mean the filament is dry, it means the air is dry, and moisture keeps crawling out of the inner windings of the spool for hours after that. For nylon, keep going 12 to 24 hours past the point the gauge bottoms out. And the little filament moisture meters sold online do not work, they read zero even on a soaked spool. Trust the scale.

One thing the tool will not do is quote you a percentage target, because for most materials the numbers do not support one. Between soaking wet and industrially dry, PLA, PETG, ABS and PC move 1 to 5 grams on a full spool, and the empty spool's weight is less certain than that (Prusa's own published spool weight has shifted by 85 grams between slicer versions). Nylon is the exception: a wet spool carries 10 to 55 grams of water, a kitchen scale sees that easily, and there is a measured defect threshold to aim at. The tool's weight card is built around exactly that split.

Drying is not permanent either. The internet quotes per-material windows with great confidence, "PETG stays dry a week", "PLA a month", and I traced the most-repeated table back to a vendor page that cites nothing for it. What is actually published: Bambu's figures of 2 to 7 days in a 20% humidity dry box, and 2 to 12 hours in ordinary room air, with no per-material split. Nylon has the one measured number, 2 to 8 hours of open air before defects, which is why it prints straight from the dryer. Set your air in the tool and it gives you the window that has a source behind it.

Does your filament even need drying?

Not all of it does, and the drying industry would rather you not know that. PLA, PETG, and ABS barely lose any strength to moisture in controlled testing. For those the only reason to dry is print quality, cleaner surfaces and less stringing, and in a dry climate like mine even that is often not worth the bother. PP, HIPS, and Polycarbonate blends are documented as not needing it at all.

The ones that genuinely matter are nylon, its carbon-fiber versions, and PVA. Peer-reviewed testing measured nylon's stiffness dropping by as much as 60 percent after a week in water, and a 71-spool study found more than half of new nylon spools already past the defect threshold straight from the sealed bag. If you print those, drying is not a nice-to-have. TPU is its own case: the strength studies do not show dry TPU winning (one found peak strength at middling humidity), so drying TPU is about clean printing, not strength. The tool flags every one of these per material.

Dryer, oven, or the AMS

A dedicated filament dryer is the simplest path, but do not take the box's number on faith. Instrumented testing measured several popular dryers well under their advertised max: one 80C model held 60C inside, and one 70C model managed 41C. The tool shows both figures where a measurement exists and grades your dryer on the measured one. Most consumer dryers top out at 70C, which is the cool end of the range for nylon and PC, workable if you give it the hours and confirm by weight. Ovens reach any temperature you need, but home ovens swing 10 to 20C above the dial below 100C, so you need a separate thermometer or you will cook PLA into a fused pancake. A food dehydrator works for the low-temperature materials and nothing hotter.

One thing about the Bambu AMS, since I run an AMS 2 Pro: it is a dry box, not a dryer. It keeps already-dry filament dry, and even then it is not airtight, humidity inside creeps up over a week if the desiccant is spent. Dry a wet spool in a real dryer first, then let the AMS maintain it. And whatever the method, airflow matters as much as heat, a well-ventilated dryer running a touch cool beats a sealed box at the perfect temperature.

Drying several materials in one box

Multi-spool dryers hold four or eight spools and their manuals say nothing about what happens when the spools disagree on temperature. The only written manufacturer rule I found is Bambu's: take the low-temperature filament out before you dry the high-temperature one. Experienced users run the same method the long way around, everything goes in at the low temperature, the low-temperature spools come out when they are done, then the heat goes up for the rest.

The tool's batch planner builds that staged schedule for you. The temperatures and ceilings in each stage are manufacturer figures; the schedule combining them is my derivation, because no such schedule is published anywhere. It also enforces the documented exceptions, BVOH's hard 16-hour cap, PC's dry-once-then-seal rule, and the materials that soften if they sit static in a hot box.