PETG

PETG (glycol-modified polyethylene terephthalate) is an amorphous thermoplastic copolyester. It is based on PET, familiar from beverage bottles, but part of the ethylene glycol in the chain is replaced with cyclohexanedimethanol (CHDM). CHDM suppresses crystallization, so the material stays transparent even in thick walls and is tougher and easier to form hot than standard PET.

PETG has a glass transition temperature of around 80 °C and an HDT of typically 65 to 70 °C, so loaded parts are designed for roughly 60 °C. Tensile modulus is about 2 GPa, tensile strength around 50 MPa and density about 1.27 g/cm³. Elongation is high, so an overloaded part tends to bend rather than snap. PETG resists water, dilute acids and bases and many oils and greases, but handles ketones and chlorinated or aromatic solvents poorly. Grades approved for food contact and for medical packaging are available.

In industry, PETG is processed mainly by extruding sheet and film, which is then thermoformed (packaging, blisters, displays, protective shields), and also by injection molding. PETG sheet forms at lower temperatures than polycarbonate, usually without pre-drying, and cuts and drills well. Compared with polycarbonate, PETG is cheaper but has lower heat resistance and impact strength. Compared with PMMA (acrylic), it is tougher but softer and scratches more easily.

For FDM 3D printing, PETG is typically printed at 230 to 250 °C at the nozzle and 70 to 90 °C on the bed. It shrinks less than ABS, usually needs no enclosure and has very good layer adhesion. That makes it a common choice for functional FDM parts when PLA falls short on heat resistance or toughness and printing ABS would be needlessly demanding.

Choose PETG for functional prototypes and FDM parts that need to be tougher than PLA and handle temperatures up to about 60 °C: brackets, covers, electronics enclosures, cable grommets, jigs and fixtures, and equipment parts for workshops or indoor use. It also works for parts in damp conditions or water contact, for translucent covers and light guides with modest optical requirements, and for parts with spring features that would crack in PLA.

As sheet, PETG is a practical material for machine guards, protective screens, clear fixture lids, packaging and vacuum-formed parts in small batches. If the part must withstand higher temperatures or heavy impacts, or meet flammability requirements, compare it with polycarbonate, ASA or PC/ABS.

PETG absorbs moisture. Wet filament bubbles and strings, and the parts have a poorer surface and lower strength, so dry it before printing and store it dry. On smooth PEI or glass build plates it can bond so strongly that it tears out part of the plate surface on removal, so a release layer is recommended. Clear filament produces only translucent parts; optically clear parts require sheet, injection molding or a polished machined part.

In a request for quote, do not confuse PETG with PET or related copolyesters such as PCTG, which have similar names but different properties. For continuously loaded parts, expect creep at elevated temperatures, and for outdoor applications, limited UV resistance of standard grades. For long-term outdoor use, choose a UV-stabilized grade or ASA.