PETG, sometimes written as PET-G, is a variant of PET, which is short for "Polyethylene terephthalate". PET is a thermoplastic polymer and the most commonly used polyester in that family. PET-G is a PET material where the ethylene glycol has been replaced with cyclohexanedimethanol, lowering its melting temperature. This makes it usable on a wide ranger of FFF printers, whose hotends are often limited to a temperature of 300°C.

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PETG is also easy to process in FFF. The mechanical properties of PETG parts are comparable to ABS or ASA parts. However, PETG lacks the thermal properties of ABS/ASA, only having slightly better thermal performance than PLA.

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The improved flexibility and overall mechanical behavior of PETG also means that support is more difficult to remove. In turn, this increases the price of PETG parts, if they require supports.

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PETG is not a bioplastic. It contains many additives that are not gathered from renewable sources.

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A well designed FFF-PETG part should be support free and warping free.