What makes PETG tougher than PLA, and where does the impact resistance come from?
PETG is PET modified with glycol, and that modification interrupts the crystallisation which leaves plain PET rigid and brittle. The result is an amorphous polymer with more give: impact energy is absorbed by deformation rather than travelling as a clean crack, and the melt flows long enough for adjacent layers to knit, so the bond between layers is stronger than in PLA. In practice a printed bracket, housing or container can flex and take a knock without splitting at the seam. The same structure makes PETG far more tolerant of moisture and many common chemicals than PLA. It remains a thermoplastic, so for parts in sustained high heat, ABS, ASA or PC are the better route.
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