A common problem with 3D printing is that nothing works, and this is often due to damp filament (at least that was frequently the case for me, especially in the early days of printing in 2015). The filament becomes damp because most plastics absorb moisture from the air, meaning they are hygroscopic (this includes, for example, PA and ABS). However, all filaments absorb moisture, at least on the surface, through their microscopically porous surface (especially PETG). This effect is very noticeable at humidity levels above 40%, increases significantly above 50%, and above 60%, printing small and fine details is usually no longer possible. To help you identify damp filament more quickly, I've put together this short guide.

Note

First, I'd like to point out that slightly damp filament doesn't cause major problems with many models and nozzle diameters, so the filament's dryness isn't necessarily relevant, especially with PLA, where this is rarely an issue. Many filaments on the market now contain additives to ensure they print well even after poor storage. However, if you want to print functional parts, it's crucial to use thoroughly dried filament to ensure the parts are stable, and this is only guaranteed with dry filament, especially with ABS, ASA, PC, Nylon, PVA, and similar materials. In my experience, problems only arise when the humidity remains above 50% for an extended period! Therefore, owners of air-conditioned printers definitely have an advantage.

At a humidity level of around 30-40%, PLA and PETG can usually be processed without problems with nozzle diameters over 0.4mm. However, this leads to increased stringing, and a powerful part cooling fan is necessary for fine details.

Anyone who wants to print very quickly with their printer should make sure to keep the filaments as dry as possible and not use "easy to print" filaments, as these are designed to be printable even with a certain amount of moisture, which, however, impairs their flow properties.

How to recognize damp filament

Clogging / Blockage:

Damp filament conducts heat better, and this can cause the filament to clogging.

The filament softens above the melting zone, and the area cools down again due to the slow pressure of the cold-end fans, causing the filament to stick in the heat brake. This blockage is called "klogging," and it can also occur if the cold-end cooling is insufficient. The rising water vapor significantly heats up the cold-end heatsink, requiring considerably more cooling power, which can be prevented by inadequate cooling. In most cases, the hot zone shifts, which is also due to a poor heat brake. I've written more about this in this article: All about Heat Brakes {article}.
Nowadays, heat brakes are of much higher quality, and the cooling of the cold end is usually very good, so the problem shouldn't occur much. However, it can still happen if the cooler gets dusty, the fan slowly loses performance, or you have a printer with an enclosed build chamber.

Warping & Curling

Moist filament has significantly less adhesion to the print bed, and so warping can occur even with PLA. With ABS and PC, warping can be so severe that you have to abort the print after just a few layers.

Curling refers to the corners that start to curl up. This problem can usually be largely avoided with PLA by extreme part cooling, but with ABS, for example, this would lead to warping of the part and the model developing cracks. Ozzen / Dripping Filament & Smoke: Since water expands when heated, the steam pushes more filament out of the hot end, which is called ozen. This is easy to observe when the hot end is warm, but the extruder isn't currently feeding filament; you can see more and more filament slowly oozing out of the nozzle. This can also be responsible for increased stringing during printing. (Note: Insufficient retraction can also cause stringing; more information can be found in the article "Calibrating FDM Printers Correctly {article}"). If you print slowly or with a small nozzle diameter, the filament may become viscous due to the water in the hotend, preventing further filament feeding. In this case, you can simply insert a thin Allen key or a metal rod with a diameter of less than 2 mm into the hotend instead of the filament. Press inwards to get the viscous filament back out through the nozzle. Afterwards, the filament can be dried and printing can continue as normal.

I have observed this effect most clearly with nylon (PA), as this plastic is very hygroscopic and absorbs moisture very quickly, even when stored properly. During extrusion, you can observe wisps of smoke and popping noises, while the filament comes out of the nozzle very unevenly.

Build chamber temperature:

The escaping water vapor introduces a lot of heat into the build chamber of a printer with an enclosed build chamber. This leads to an excessively high internal temperature, and the cold end often cannot be cooled properly, resulting in clogging or stepper motors overheating and missing steps.
It should also be noted that higher temperatures are required to ensure the same filament flow.

Odor:

Anyone who uses wet Anyone printing with filament can recognize this by the significantly stronger odor, especially with ABS, HIPS, PC, etc., because most filament types can be processed dry with the correct settings (not too hot) and are almost odorless.

Appearance:

You can't tell from the filament itself whether it's dry or damp, but when you push it through the nozzle, you can see water vapor rising from very damp filament (especially PA or Woodfill), and in extreme cases, the filament comes out bubbling and looks spongy when cooled.
The absorbed moisture affects the diameter and weight of the filament; that is, it becomes thicker and heavier. Due to poor storage, it is usually unevenly moist, and therefore the diameter varies. strong.

Printed part:

During printing, the filament will adhere poorly to the print bed. This effect is particularly pronounced with ABS when it is damp. Printing very slowly or using various adhesion sprays can sometimes work, however, the plastic will remain warm for a long time, causing corners to curl up. This makes overhangs almost impossible to print, and with ABS, PA, PC, and HIPS, warping and curling (the corners curling up) can occur. With wet filament, the water inside the filament heats up and becomes trapped in the printed part. This causes the workpiece to cool down very slowly, as the water retains the heat, keeping the printed part rubbery and elastic for a very long time. Mechanical: Printed parts made from wet filament have significantly lower load-bearing capacity and are considerably more elastic due to their sponge-like structure. Since the plastic cools down more slowly, the layer adhesion is usually very good.

I recommend that anyone who wants to manufacture functional parts, especially with ABS, PETG, PC, and PA, ensure that the filament is processed dry.

How to prevent the filament from getting damp

Upon delivery

Most manufacturers package a new spool of filament with a silica gel pouch (more information on silica gel below) together in an airtight and usually vacuum-sealed bag. Many of these pouches have a closure, so the filament can be resealed airtight after use. The bag protects the filament not only from moisture but also from dust, which adheres to the filament due to electrostatic charge and can then settle in the hot end, leading to clogging. Silica gel: Silica gel should be familiar to anyone with an FDM 3D printer, as these are the small packets that come with every spool of filament. They have the property of absorbing or releasing moisture, depending on the ratio of silica gel to air. Therefore, these pellets are ideal for drying filament. To dry the filament as effectively as possible, the silica gel can be heated in the oven at up to 150°C (I recommend a maximum of 100°C) or in a microwave on the lowest setting for about 5 minutes. If you simply leave the pellets in the oven/microwave without turning the bags, the drying effect is not as strong, or it takes significantly longer, especially if you want to dry a lot at once. Less is more here; that is, don't use too many pellets or stack the bags on top of each other, as only the outer ones will dry. More details on how I use it can be found in Oven Update 2. When using silica gel packets, it is essential to avoid using color indicators, as these will only show the drying time too late. 1. Ikagel is moist, to ensure truly dry filament, and 2. it's rather questionable from a health perspective, and we already inhale enough unhealthy fumes while printing. (more on this in the post Staying healthy when printing (still in progress))

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Storage

Airtight containers protect the filament from humidity during storage or transport. Filaments should not be exposed to excessive heat or cold, or to direct sunlight. In Bags Bags are a very inexpensive and easy way to store filament. There are small bags that are precisely sized for the spool, or large bags that are actually designed for blankets and clothing. The only disadvantage of these bags is that you have to be very careful not to puncture them by bumping the filled bag against a sharp object, or by packing the filament so awkwardly that the end of the filament pokes through the bag. Unfortunately, I've also found that the closure wears out over time, and the bag slowly refills with air. If the bag becomes dirty, it can also become less airtight, which would then also contaminate the filament and, as already described, lead to clogging.