PEI sheet

A PEI sheet is a build surface material, usually a thin sheet applied to a spring steel or aluminum plate, known for a useful property: it bonds well to plastic like PLA or PETG while the bed is hot, then lets go on its own as the plate cools, often popping prints free with a light flex instead of scraping.

PEI comes in smooth and textured finishes. Smooth PEI gives a glossy bottom surface and very strong grip, which can occasionally be almost too strong for certain filaments unless a bit of glue stick is used. Textured PEI gives a slightly matte, patterned bottom finish and is often more forgiving for warping-prone materials because it grips broadly rather than at a few sharp points.

A PEI sheet needs occasional cleaning with isopropyl alcohol, since skin oils and dust reduce its grip over time, and it eventually wears out after enough prints. A common mistake is leaving fingerprints across the surface right before a print, or continuing to use a heavily scratched, worn sheet and blaming filament or the printer for adhesion problems that are actually caused by a tired surface.