PEI build plate: a surface that grips and lets go

What PEI is

PEI stands for polyetherimide, a hard, heat-resistant plastic. On a build plate it is applied as a thin layer on a flexible steel sheet. The sheet is normally attached by magnets to a heated base and can be taken off it.

The principle is simple: when the plate is hot, plastic sticks to it well. When it cools, the grip drops and the part releases, often by itself. With rigid parts you flex the sheet a little and the part peels off. It is an ordinary build plate.

Smooth or textured

Smooth PEI gives the underside of the part a glossy finish. Textured PEI has a fine grainy surface which is imprinted into the underside. That kind of surface hides small flaws better and grips well, which is why it is very popular with both PLA and PETG.

With PETG you need to be careful on smooth PEI: the plastic can stick too well, and tear pieces off the surface when it is removed. That is why a release layer, such as a thin coat of glue stick, is often used on smooth PEI.

Care, and what the customer gets from it

• Cleanliness. Grease from fingers makes adhesion worse. The plate is cleaned with isopropyl alcohol or warm water with washing-up liquid.
• Wear. After many prints the surface wears down and plastic stops sticking to it (adhesion). The whole sheet is then replaced.
• For you. When ordering, you do not have to think about the plate. The imprint of its surface will be visible on the underside of the part, so rotate the model so that the most important face points up.

Why PEI replaced older surfaces

Before PEI, people used glass with glue or masking tape. Both worked, but they needed preparing before every print and wore out after a while. PEI on a flexible sheet is ready at once, nothing has to be applied and the part can be released with a single flex.

Plastics stick to PEI with different strength. PLA holds well at around 55 to 60 °C, while PETG is harder because of the strong adhesion mentioned above. That is why the plate temperature setting differs for each material and follows the filament maker's recommendations.