Does PLA shrink in the cold? Freezer and winter math

Yes, but only slightly, and it comes back. A 100 mm part in PLA (polylactic acid) gets 0.16 to 0.38 mm shorter going from a 20 °C room into a -18 °C freezer, and returns to its original length once it warms up. PETG (glycol-modified polyester) behaves the same way and shrinks about 0.19 mm over the same drop.

How much does PLA shrink in the cold?

A PLA part shrinks by its length times its thermal expansion coefficient times the temperature drop. PLA data sheets list 41 to 101 millionths per °C, so a 100 mm part taken from a 20 °C room to a -18 °C freezer gets 0.16 to 0.38 mm shorter. It regains that length as it warms back up.

contraction = length x CTE x temperature drop

Freezer, low end:  100 mm x 0.000041 /°C x 38 °C = 0.16 mm
Freezer, high end: 100 mm x 0.000101 /°C x 38 °C = 0.38 mm

The spread comes from the data sheets. SD3D’s PLA sheet lists a coefficient of thermal expansion (CTE) of 41 × 10⁻⁶ per K, and SUNLU’s lists 101 × 10⁻⁶ per °C. Ultimaker’s PLA sheet leaves the field blank. Use the high end when a fit must not bind, or measure your own spool (below).

The FDA puts a home fridge at 40 °F (4 °C) or below and a freezer at 0 °F (-18 °C). Starting from a 20 °C room:

Where the part goes	Temperature drop	PLA, per 100 mm	PETG, per 100 mm
Fridge, 4 °C	16 °C	0.07 to 0.16 mm	0.08 mm
Winter garage, -10 °C	30 °C	0.12 to 0.30 mm	0.15 mm
Freezer, -18 °C	38 °C	0.16 to 0.38 mm	0.19 mm

The change scales with length. A 20 mm feature moves a fifth as much: 0.03 to 0.08 mm in the freezer.

Making a part the right size when cold

If a part must hit a dimension at freezer temperature, scale it up by the contraction. A 100 mm lid that must measure 100 mm at -18 °C needs 0.16 to 0.38% added. Enter that percentage in the shrinkage compensation calculator on top of your normal print shrinkage; it multiplies the two steps correctly.

Does PLA go back to its original size after the freezer?

Yes. Cold contraction is reversible: the part grows back as it returns to room temperature. Permanent size change in printed PLA starts near its glass transition, about 60 °C. Bute et al. (2024) measured irreversible strain that built up between there and 80 °C. A freezer sits about 80 °C below that point, so freezing does not reshape the part.

Heat is different. In the same study, printed PLA heated to 80 °C kept 8 to 9% permanent strain.

Measure only after the part has warmed fully, the same rule as for print shrinkage. A part pulled from the freezer and measured at once reads small.

Does PETG shrink in the cold?

Yes, by about the same amount as PLA. Eastman’s data sheet for its Eastar 6763 copolyester lists a CTE of 51 × 10⁻⁶ per °C, measured from -30 °C to 40 °C, so the figure covers freezer temperatures. That gives 0.19 mm on a 100 mm part from 20 °C to -18 °C, and the part regains it when warm.

That is a resin data sheet, not a printed part. Ultimaker’s PETG filament sheet leaves CTE blank, as its PLA sheet does.

Will a cold PLA part still fit a metal shaft or bolt?

PLA contracts 3 to 9 times as much as steel and 2 to 4 times as much as aluminum. Engineering ToolBox lists steel at 10.8 to 12.5 × 10⁻⁶ per °C and aluminum at 23 × 10⁻⁶ per °C.

• PLA around metal tightens. A 20 mm PLA bore on a 20 mm steel shaft shrinks 0.03 to 0.08 mm in the freezer, while the shaft shrinks about 0.01 mm. The fit closes up by 0.02 to 0.07 mm. A sliding fit with 0.1 mm clearance still slides; a press fit gets tighter.
• PLA inside metal loosens. A PLA peg in a steel or aluminum hole loses the same 0.02 to 0.07 mm of grip and can rattle.

Snap fits and threads move by the same fractions: 0.01 to 0.02 mm on a 6 mm feature.

Does cold make PLA or PETG brittle?

PETG gets less impact-resistant in the cold. Eastman’s 6763 sheet drops notched Izod impact from 101 J/m at 23 °C to 37 J/m at -40 °C. Spectrum’s PETG filament sheet drops from 120 J/m to 55.5 J/m.

For PLA, no data sheet checked here gives impact values below 23 °C. In a slow pull, printed PLA got stronger in the cold. Karimi et al. (2023) found its tensile strength fell 55 to 75% as test temperature rose from -20 °C to 40 °C. That is strength, not toughness against a knock. If a frozen PLA part has to survive a drop, test a sample straight from the freezer.

How do you measure the shrinkage on your own spool?

1. Print a bar about 100 mm long; longer spans make the change easier to read.
2. Let it sit at room temperature for a few hours, then measure it with digital calipers and note the room temperature.
3. Freeze it for a few hours and measure it straight away, within seconds, before it warms.
4. Divide the change by the length and the temperature drop. A 0.25 mm change on 100 mm over 38 °C gives 66 × 10⁻⁶ per °C.

Keep the calipers at room temperature, not in the freezer with the part. The dimensional accuracy calibration guide covers measuring technique for printed parts.