ASA shrinkage: how much it shrinks and how to compensate

ASA shrinks about 0.4 to 0.7% in typical FDM printing. INEOS Styrolution, who make the Luran S ASA resin, state a processing shrinkage of "usually 0.4 to 0.7%" on their datasheet, which lines up well with what makers measure on printed parts. That puts ASA right alongside ABS near the top of the common filaments, though it tends to warp a little less.

A quick clarification before the numbers. What a maker cares about is the dimensional error on the actual printed part, measured with calipers once it cools. That is not the same as the "mould shrinkage" a datasheet quotes for injection molding, though in ASA's case the two happen to sit in a similar band. Most FDM filament datasheets (Prusament, Polymaker) don't publish any shrinkage figure at all, so measuring your own prints is still the reliable move.

Why ASA behaves like ABS

Thermoplastics contract as they cool from print temperature back to room temperature, and the size of that contraction tracks the glass-transition temperature (Tg) and the print-to-ambient temperature drop.

ASA is chemically close to ABS: amorphous, so it doesn't crystallize, with a high Tg around 100°C. That high Tg means a large temperature drop from nozzle to room, which is what pushes both materials toward the top of the shrinkage ranking. The main practical difference is that ASA, designed for UV and weather resistance, usually warps somewhat less than ABS, even though its raw shrinkage is in the same neighborhood.

A few points that apply to ASA like any FDM material:

• Shrinkage is anisotropic. It's larger in X and Y than in Z, and holes and inner contours come out undersized more than the outer walls.
• It grows with part size. At 0.6%, that's 0.12 mm on a 20 mm feature but 1.2 mm across a 200 mm part.
• Warping is separate from shrinkage. Warp is corner curl from uneven cooling, not a uniform size change. ASA warps less than ABS but still wants an enclosure for anything sizeable.

How ASA compares to PLA, PETG, and ABS

Here's where the four common filaments land, most shrinkage to least. The ordering follows glass-transition temperature and the print-to-ambient drop, not crystallinity, since all four print effectively amorphous.

ABS and ASA sit together at the top, PETG in the middle, PLA at the bottom. If you already have ABS compensation dialed in, your ASA values will be close, though it's still worth calibrating each filament separately.

How to compensate

For ASA, like ABS, compensation is worth doing on any part with a real fit. The workflow:

1. Print a calibration object in the same thermal setup you'll use for the real part, enclosure and all. A 100 mm cube keeps the math simple.
2. Measure with calipers after it has fully cooled. Measure X, Y, and Z separately.
3. Convert each measured shrinkage into a scale factor.

The formula:

scale% = 100 / (100 − shrink%)

A measured 0.6% shrinkage means scaling to 100 / (100 − 0.6) = 100.6%, or ×1.006, inside the ASA window above.

Our material shrinkage calculator takes either a shrinkage percentage or your measured-vs-expected dimensions and returns the scale factor plus the slicer compensation value. Its ASA default is 0.5%, which sits inside the typical range here. Since ASA holes shrink more than outer walls, use the XY hole-compensation idea the calculator supports for anything with tight bores or press fits, and set per-axis values rather than one uniform number when the part demands it.

Related reading

Change material and both the numbers and the warp behavior shift. Here are the siblings to this guide:

• PLA shrinkage
• PETG shrinkage
• ABS shrinkage

Printing ASA usually means an enclosure and some tuning. Our roundup of free 3D printing tools and calculators covers the flow, temperature, and calibration tools that pair well with shrinkage compensation.

Let GrandpaCAD size the part for you

Compensation is scaling, and per-axis scaling is tedious by hand. Describe the part in plain English, tell GrandpaCAD the material and the fit you need, and it can model the geometry pre-scaled to compensate, so the ASA part comes off the bed at the size you intended.

Sources and further reading

• INEOS Styrolution: Luran S ASA product page and datasheets
• PlastikCity: material shrinkage rates
• Bambu Lab forum: combatting hole shrinkage, with data