Cleaning the PEI flex steel print sheet

The Prusa i3 Mk3 printer ships with a PEI-coated flex steel print sheet. The surface has excellent adhesion properties for most materials, but does require some basic maintenance. Without good first layer adhesion, you’re going to have a difficult time achieving good print results. It’s worth spending some time getting familiar with the bed characteristics when starting out.


These notes are based on my experiences with the Prusa i3 Mk3 printer. If you are using a different printer, please verify the hardware details are same. These pages may be a bit rough as I revise them and add new material. Please check back regularly for updates.

Understanding the PEI sheet and adhesion

The PEI sheet used on the Mk3 is a wonder. When properly cleaned and cared for, printed parts will stick firmly enough to get a solid print, yet pop off easily when cooled. What’s often not understood is that you have to maintain the PEI surface to get the best results.

Your Prusa flex steel PEI sheet is not just another print surface

The first thing to understand is that PEI is very different than most other print surfaces. Do some searching on the internet and you’ll find hundreds of articles on using glue stick, hair spray, glass sheets, blue painter’s tape, sugar syrup a host of other solutions. Ignore these. They’re usually written for printers that require manual bed leveling, ship with warped parts other shortcomings.

The one and only trick to PEI is to keep it clean. How do to this depends on just how contaminated the surface is. The biggest enemy is grease, and the biggest source of that grease is your fingers as you handle the sheet. No matter how you clean your sheet, try to avoid touching the PEI surface as much as possible.

Cleaning the PEI print surface

Under normal circumstances, your cleaning routine should be as simple as:

  1. Give the bed a wipe with 91%+ isopropyl alcohol. Not necessarily every print, but any time you think you might have touched the sheet or otherwise contaminated it. Weaker strengths of alcohol may work, but stronger concentrations simply do a better job of dissolving grease.
  2. If isopropyl alcohol fails, try a wipe with 100% acetone. This isn’t recommended every print because it can eventually cause cracking of the PEI, but it rejuvenates the PEI surface. Consider a wipe every month or so for conditioning.
  3. If isoproply alcohol and acetone don’t work, there’s a good chance there’s enough build-up of gunk that you’re simply moving it around. Take the sheet to your kitchen sink and give it a good was with Dawn dish soap or your local equivalent. Use a clean paper towel to clean it and another to dry it.
  4. Finally, if the other measures are not sufficient, you can try a buffing with a 3M 7445 Scotch Brite pad.

Above all else, avoid touching the PEI surface. With a good clean and a proper Live-Z calculation, you should have no problems with adhesion.

Dealing with over-adhesion

Some materials like PETG grip a bit too well to the print surface. If printing with these materials, you want to use something to lessen the grip. Prusa recommends the following:

  1. For “normal” sticky materials, you need to use something to loosen the adhesion.

    1. A wipe of the PEI surface with Windex or your local equivalent of window cleaner will work. Don’t use anything enhanced with vinegar or anti-streaking agents. The key is that this cleaner leaves a very thin residue that helps remove materials that otherwise stick a bit too well.
    2. Simply wiping the print area with your fingers can work well. Not too much, but enough to interfere with the adhesion.
  2. For high-temp sticky materials, you may need a better relese agent.

    1. A thin layer of glue stick on the print area will help pop parts off. You don’t want to use too much, and it will eventually build up and require a good cleaning under the sink (see above).
    2. I’ve had good luck using MagiGoo on the PEI. The applicator allows applying a precise thin layer exactly where it’s needed. It’s still a bit messy and requires eventual clean-up, but not as bad as glue stick. MagiGoo is a bit expensive, but a small bottle goes a long ways.

Finally, take advantage of the removable flex surface to pop prints off. You can use a non-metallic scraper to help lift prints that stick a bit.

If you’re careful, won’t need to clean the bed every print.

Contact and feedback

You can find me on the Prusa forums or Reddit where I lurk in many of the 3D printing-related subreddits.

Last updated on Mar 18, 2019