How to design FDM parts that resist warping and shrinkage
Warping and shrinkage in FDM come from thermal contraction, not bad luck. Learn the geometry and material choices that keep parts flat.
Warping is the lifting or curling of a printed part away from its intended shape, usually starting at the corners of the build plate or developing along a long flat span after the part is removed from the machine. Shrinkage is the underlying cause: every thermoplastic contracts as it cools from extrusion temperature to room temperature, and if that contraction is uneven across the part, the geometry pulls itself out of shape.
This guide covers why warping happens and which levers reduce it: material choice, wall geometry, orientation and bed adhesion strategy. The other guides in this cluster go deeper on specific materials and on large or long parts.
Why shrinkage turns into warping
A part does not cool evenly. The first layers on the build plate stay close to bed temperature for the whole print, while later layers cool in open air as soon as the nozzle moves on. This creates a temperature gradient through the height of the part, and each layer shrinks a little differently as it drops to ambient. The result is internal stress: the outer layers try to contract more than the layers still attached to a warm base allow, and that stress bends the part upward at its edges once the restraining force of adhesion is exceeded.
Amorphous materials like ABS and ASA shrink more and more unevenly than semi-crystalline materials like PLA, because they have a wider, less sharply defined transition from soft to solid. Semi-crystalline materials like PA12 and PA6 shrink less on cooling but absorb moisture afterwards, which introduces a second, slower dimensional change that behaves differently again. Understanding which mechanism dominates for a given material tells you which fix actually helps.
| Material | Shrinkage tendency | Main risk |
|---|---|---|
| PLA | Low | Rarely warps except on very large flat parts |
| PETG | Low to moderate | Corner lifting on large parts without an enclosure |
| ABS | High | Corner lifting, layer splitting on tall parts |
| ASA | High | Same as ABS, slightly better outdoor stability |
| PA12 / PA6 | Moderate on cooling, plus moisture growth | Dimensional drift over weeks if not sealed |
| PC | High | Needs enclosed, heated chamber to print flat |
Geometry decisions that reduce warping
The single biggest geometric driver of warping is the size of the flat area in contact with the build plate. A large, uninterrupted footprint accumulates more shrinkage stress across its width than a broken-up one, because the shrinkage of every point on that surface pulls in the same direction toward the centre. Splitting a large flat base into ribs, or adding a slight arch or radius instead of a dead flat underside, gives the stress somewhere to redistribute instead of concentrating at the corners.
- Avoid sharp 90 degree corners on the outline in contact with the bed; a small radius or chamfer reduces the local stress concentration
- Break up large flat faces with ribs, pockets or a honeycomb underside rather than leaving one continuous plane
- Keep wall thickness as uniform as possible; thick sections cool slower and shrink after thin ones have already solidified
- Add a brim or raft on materials prone to lifting instead of relying on adhesive alone
- Orient tall thin parts so the largest flat face is not the one on the bed if warping has been an issue before
- Where possible, design a slightly convex or ribbed underside instead of a perfectly flat one on large panels
Process and material levers beyond geometry
Bed adhesion and chamber temperature matter as much as geometry for the materials most prone to warping. ABS, ASA and PC benefit from an enclosed, heated build chamber that keeps the ambient air around the part close to its glass transition temperature, slowing the cooling gradient that creates stress in the first place. PLA and PETG rarely need this and print acceptably flat on an open machine with a heated bed alone.
Material selection itself is often the more cost-effective fix than fighting a difficult material with process tricks. If a part does not strictly need the heat resistance of ABS or ASA, a PETG or a glass or carbon filled variant can hit the same mechanical target with far less warping risk and no enclosure requirement. That trade-off is worth raising early, before a design is locked to a material chosen for reasons unrelated to printability.
- Problem
- Corners lifted 1.5 mm off the bed on every print attempt, making the mounting face out of tolerance.
- Change
- Added 3 mm corner radii to the base outline, split the flat underside into a ribbed pattern, and switched to ASA with a brim.
- Result
- Corner lift dropped to under 0.2 mm, within the standard tolerance for the mounting interface.
Checking a part for warping risk before it is quoted
- Identify the largest continuous flat face and check whether it is the intended build orientation
- Check wall thickness uniformity across the part; flag sections thicker than about three times the nominal wall
- Confirm the material choice against the part's actual thermal and mechanical requirements, not just habit
- Add corner radii or ribs to any large flat base before the first sample is printed
- Plan for a brim, raft or enclosure on ABS, ASA or PC parts rather than discovering the need after a failed print
Frequently asked questions
- Can warping be fully eliminated with the right slicer settings alone?
- Settings like bed temperature, brim and print speed reduce warping but cannot remove the underlying stress if the geometry concentrates it in one area. Large flat parts in ABS or ASA usually still need a geometry or material adjustment alongside process tuning.
- Why does PLA warp much less than ABS?
- PLA is semi-crystalline with a lower and more gradual shrinkage across its cooling range, while ABS is amorphous and contracts more sharply through a wider temperature band. That makes ABS parts build up more internal stress for the same geometry.
- Does adding a brim always solve corner lifting?
- A brim increases the effective footprint and adhesion area, which helps on moderate cases, but on parts with a strong stress concentration in one corner it only delays the lift rather than removing the cause. Geometry changes are the more reliable fix for series production.
- How much shrinkage should we expect across a 200 mm part?
- As a rough order of magnitude, PLA and PETG shrink well under 0.3 percent linearly, while ABS and ASA can reach 0.5 to 0.8 percent depending on geometry and cooling. On a 200 mm length that is roughly 0.6 to 1.6 mm of potential dimensional change, which is why compensation and orientation matter on long parts.
- Is nylon warping the same phenomenon as ABS warping?
- The cooling mechanism is similar but nylon adds a second effect: it absorbs ambient moisture after printing and swells slightly over days to weeks. A part can look flat straight off the printer and still drift dimensionally afterward, which is a separate issue from thermal warping.
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ABS and ASA reward parts designed with their thermal behaviour in mind and punish parts that are not.
Designing parts for PA12, PA6 and nylon
Nylon parts behave well mechanically but need a design that accounts for moisture uptake, not just cooling shrinkage.
Large flat areas and long parts
The larger a flat area or the longer a part, the more every small percentage of shrinkage turns into millimetres that matter.
Material selection as a DFM decision
The right material choice can fix a warping problem, a tolerance problem and a cost problem at the same time.
Wall Thickness for FDM Parts: The Complete Guide
Wall thickness is the single design decision that most affects strength, cost and print reliability in FDM parts.