How to replace and care for PEI foil

23. 05. 2023

Possible causes of damage

There are two typical reasons for PEI foil damage :

• the printed parts are fused to the PEI foil and when the print is removed, part of it is torn off
• the print nozzle gets too close to the print bed and damages it

Removing prints with a metal spatula can sometimes cause scratches or other damage to the surface of the PEI film. And the prints that stick to the PEI foil can sometimes come off along with part of the foil.

On Original Prusa 3D printers, it can cause a problem if the PINDA flatness sensor is set too high, the nozzle can damage the PEI film during XYZ calibration.

Possible ways to avoid damage

Correct height adjustment of the PINDA sensor

There are ways to prevent damage to PEI film, as well as ways to maintain its surface. As soon as the foil is damaged to the extent that there are areas that are no longer suitable for printing, a replacement of the foil is in order.

Especially if you are assembling the Original Prusa printer yourself, it is easy to make a mistake in the PINDA sensor settings. After assembling the printer, you usually need to set the first layer. Which is better to do with caution than to regret the damage caused later. The PINDA sensor detects the printing pad and sets the initial height of the nozzle. After that, further calibrations are made, but if the PINDA sensor is much higher than the nozzle, then by the time the PINDA sensor detects the bed, the nozzle is already touching the PEI film. Which could mean that the nozzle will scratch the surface of the film. Especially because when calibrating, the Original Prusa i3 3D printer tends to make a lot of repetitive movements with the print head. 

In that case, it's a good idea to have your finger ready on the power button so you can quickly cut power to the printer if the nozzle makes contact with the print pad. This will prevent damage to the mat. If the nozzle is too low, following the calibration instructions and placing a sheet of paper on the print pad can help protect the print pad during calibration. If the nozzle is touching the sheet of paper at the beginning of printing, the best thing to do is to reduce the power and adjust the PINDA sensor

Pay attention to gluing the prints to the PEI foil

We already know that PEI foil can be easily damaged if we have a wrongly set sensor of the flatness of the substrate. Another way the film can be damaged is if you print from a flexible material and the print sticks to the film.

You can prevent this by using a glue stick with glue specially designed for treating the mat. But be careful, even that may not be enough. Consideration should be given to using blue tape, which is great for printing flexible materials that are known to stick easily to PEI foil.

Applying a lot of glue seems to work well too. So don't skimp on it. It is recommended to clean the pad between prints and reapply fresh glue.

Replacement of PEI film 

Changing the PEI film is actually not complicated at all. Detailed instructions can be found here . Here's a quick guide on how to do it:

Pruša's method

• turn off the printer
• remove the print pad from the printer
• place the printing pad in the freezer
• after freezing, remove the PEI foil (freezing makes it easier to release the PEI foil from the glue)
• soak a paper towel in glue remover (such as D'Limonene) and place it on the printing pad
• put the printing pad together with the paper towel in a plastic bag to prevent the glue remover from drying out
• leave it like this for about 40 minutes for the glue to dissolve
• scrape the adhesive off the printing pad
• repeat applying the adhesive remover and scraping the pad until the surface is clean
• wipe the printing pad with an alcohol-based liquid (eg IPA or white spirit ) to remove grease
• stick a new PEI foil

This method works without a problem. But while removing the print pad isn't difficult, it's a bit more time-consuming and requires tinkering with the electronics at the control board. Instead of D-Limonene glue remover, you can also use the Goo Gone brand, which has a citrus ingredient and works great too.

If you are replacing the PEI foil that came with the basic equipment of the Prusa 3d printer, please note that the foil is quite thin (0.175 mm) and if you try to remove the foil without first freezing it, it is possible that the foil will tear into small pieces. Therefore, consider whether it would be better to purchase a foil with a greater thickness. In this case, you can skip some steps during the exchange.

Some users do not remove the printing pad from the printer when changing the PEI film, but simply leave it mounted and follow the second instruction above. Even though the adhesive on the foil sticks well, with thicker foils, it is likely that a larger part will come off in one piece. Therefore, if you are removing thinner foils, it is better to use the instructions with freezing the pad. If you are removing a thicker foil, you can skip this step.  

Applying the new PEI film takes place by removing a small part of the protective film from the shorter side and pressing it onto the printing pad. Then you slowly remove the protective film and press the PEI film onto the mat. Once done, cut off the excess foil with a knife.

To additionally smooth the PEI film, you can use a plastic scraper that you wrap in a cloth so as not to damage the new PEI film. Průš's first method to remove the film is a more thorough way to achieve your goal, but if you leave the print pad mounted on the printer, you will save a good 30 minutes. Which can come in handy if you're going to do PEI film replacement as "regular maintenance" for your printer.

Maintenance of PEI film

If the surface of the PEI film is in good condition, but some parts are not sticking as well as before, there are a few things you can do to improve the adhesion. The first thing you need to do is make sure your printing pad is set up straight and the first layer is flush against it. If calibration is not a problem and the PEI film seems to have lost its grip, you can try this method:

Clean the print pad with warm water - this works especially well if you've used glue on PEI. You can also use dish soap (e.g. Dawn brand) to remove grease.

Sand the pad with fine sandpaper (grit 1000-2000). The intention is to roughen the surface a bit, not smooth it. You can achieve this by repeating short strokes in one direction, for example from back to front and then repeating from left to right. When you roughen the surface, the plastic is more likely to stick to the pad. After sanding, clean the entire pad with an alcohol-based product, such as using paper coffee filters.

This method can restore the pad to its original adhesion. During printing, try not to touch the printing pad, and when printing with PLA material, the surface of the PEI film is essentially maintenance-free. The tip for cleaning with coffee filters came from 3D printer users, and it makes sense because the filter is lint-free, disposable, and very cheap. You can pour an alcohol-based liquid, e.g. IPA, into a bottle with a pump and apply it to the filter with just a few presses of the pump.

With the advent of new spring steel printing pads, replacing the entire steel plate will become more common. But even for those who haven't switched to this type yet, changing and maintaining PEI foil can be relatively easy. And since most steel sheets still come with PEI foil, information and tips on how to maintain it can still come in handy.