Does PETG shrink? How much, and compared with PLA

Yes, PETG (glycol-modified polyethylene terephthalate) shrinks, but by less than 1%. Printed PETG parts lost 0.54 to 0.76% in X and Y and 0.73% in Z in a Binghamton University study. That is slightly more than PLA (polylactic acid) in X and Y and slightly less in Z.

How much does PETG shrink?

PETG shrinks by less than 1% as it cools. A Binghamton University study of printed parts measured 0.76% in X, 0.54% in Y and 0.73% in Z. In X and Y, a 100 mm part came out 99.2 to 99.5 mm long. Sunlu lists 0.1 to 0.5% for its PETG without naming a method.

Source	What was measured	PETG shrinkage
Weiser et al., Binghamton University (2021)	Printed parts, by axis	X 0.76%, Y 0.54%, Z 0.73%
Sunlu	Method not stated	0.1 to 0.5%

The Binghamton team printed three part designs three times each on a QIDI X-One2 and measured them with digital calipers. That is one printer and one set of settings, so treat the figures as a starting point.

Several PETG data sheets carry no shrinkage figure: Prusament PETG, Bambu Lab PETG Basic and Polymaker PolyLite PETG. Eastman’s sheet for Eastar 6763, an amorphous copolyester based on polyethylene terephthalate, lists no mold shrinkage either.

Why PETG shrinks so little

PETG is amorphous. Eastman describes Eastar 6763 that way, and Polymaker’s annealing guide classes PETG as amorphous too. Its chains stay disordered as it cools, so it only contracts thermally. Semi-crystalline plastics such as nylon also pack chains into ordered regions as they cool, which removes extra volume.

The same small contraction keeps PETG flat. Prusament credits its low thermal expansion and says PETG “rarely lifts from the bed and warps” even on big objects without an enclosure.

When PETG shrinks

PETG shrinks as it cools, from the moment it leaves the nozzle until the part reaches room temperature. A part measured warm reads large, so let it cool fully first.

Does PETG shrink more than PLA?

Slightly more in X and Y, slightly less in Z. In the Binghamton printed-part study, PETG shrank 0.76% in X and 0.54% in Y against 0.63% and 0.35% for PLA. In Z it lost 0.73% against PLA’s 0.80%. On a 100 mm part the gap is 0.1 to 0.2 mm, small enough for your settings to reverse.

Axis	PLA	PETG	Difference on 100 mm
X	0.63%	0.76%	PETG 0.13 mm smaller
Y	0.35%	0.54%	PETG 0.19 mm smaller
Z	0.80%	0.73%	PETG 0.07 mm larger

Sunlu’s figures also put PETG a little higher: 0.1 to 0.3% for its PLA and 0.1 to 0.5% for its PETG. The ranges overlap, so a given PETG spool can shrink less than a given PLA spool.

By the Binghamton figures, a PLA shrinkage value puts PETG within 0.2 mm per 100 mm. If a fit matters to a tenth of a millimeter, measure each filament separately.

What shrinkage value should you enter for PETG?

Start with 0.65% in X and Y and 0.73% in Z, the Binghamton PETG averages. Enter 99.35% (XY) and 99.27% (Z) in OrcaSlicer, 99.35% in Bambu Studio, or 0.65% and 0.73% in PrusaSlicer. Then print a test part in your own PETG and replace these with what you measure.

The 0.65% is the mean of the study’s X (0.76%) and Y (0.54%), because slicers take one XY value. Each slicer phrases the field differently:

Where	Field	XY value	Z value
OrcaSlicer	Shrinkage (XY), Shrinkage (Z)	99.35%	99.27%
Bambu Studio	Shrinkage	99.35%	none; scale Z to 100.74%
PrusaSlicer	Shrinkage compensation XY, Z	0.65%	0.73%
Model scale tool	Scale	100.65%	100.74%

• OrcaSlicer and Bambu Studio want the cooled size as a percentage of the design. The default is 100%, which means no compensation.
• Bambu Studio scales X and Y only, so put a Z correction on the object’s scale.
• PrusaSlicer wants the shrinkage itself, so a part that measures 99 mm on 100 mm gets 1%. It shows the fields in Advanced and Expert mode.
• The model scale is 1 ÷ (1 − shrinkage). Use it only if the filament profile is left at no compensation; doing both corrects the part twice.

How to measure your own PETG

Set compensation to none, then print a block about 100 mm long and 20 mm tall in your PETG with your normal temperatures and cooling. Measure X and Y separately at room temperature, mid-face rather than at the corners. Measure Z without the first layer’s bulge.

The shrinkage compensation calculator turns the designed and measured sizes into each slicer’s values. The guide to calibrating dimensional accuracy per material covers flow and hole errors to rule out first.

Z needs more care than XY. Layer height and first-layer squish move the Z reading, so a Z figure from another printer transfers less well than an XY one.

Annealing changes the size again (Prusa’s tests saw PETG shrink along its longest dimension and grow in Z), and the calculator can stack that step on top.