3D Printing Shrinkage: Causes and Solutions

SLA 3D printing (stereolithography) benefits from a fundamentally different curing process. Instead of relying on heated extrusion and thermal cooling, SLA uses photopolymerization, which results in more predictable behaviour and tighter tolerances.

The main cause of shrinkage in 3D printing is the contraction of the material as it solidifies. This contraction occurs for different reasons depending on the printing technology:

• In FDM/FFF, shrinkage is mainly thermal. The polymer cools from 200–300 °C (392–572 °F) to room temperature, and this temperature drop causes the part to contract, often resulting in warping or dimensional deviation.
   
• In SLA, shrinkage is primarily chemical. When liquid resin cures under UV light, the polymer network forms and the volume decreases. The reaction produces only mild heat, so thermal effects are minimal and overall shrinkage is smaller and more predictable than in FDM.

• Shrinkage in resin printing can be measured using a volumetric density technique. First, determine the density of the uncured liquid resin and the density of the cured solid. Then calculate shrinkage using the formula:
   
• Shrinkage (%) = (1 – (rho_liquid / rho_solid)) × 100, where:
  • rho_liquid = density of the uncured resin (g/cm³)
  • rho_solid = density of the cured polymer (g/cm³)

Shrinkage may appear immediately after printing, but it often becomes more visible during post curing where the conversion of the system increased to its limit. It means when additional crosslinking increases the total polymerization shrinkage. 

The example below shows the difference between a low shrinkage monomer and a higher shrinkage monomer.

FDM relies on thermal adhesion between layers, which makes some layers weaker or more prone to distortion. SLA creates layers by curing entire regions of resin uniformly for consistent structural integrity. This uniform bonding minimises anisotropic shrinkage, where one direction contracts more than another, and gives SLA parts a more stable dimensional profile and smoother surfaces.

SLA support structures are thin, rigid, and strategically placed to counteract gravitational and curing forces. Because 3D resins cure in a liquid bath, parts remain supported from all sides, which prevents sagging or curling. 

This controlled environment ensures that delicate or tall components stay dimensionally accurate throughout printing, unlike FDM, where supports often introduce thermal stresses.

SLA printers operate in enclosed chambers with stable temperatures, minimal airflow, and controlled humidity. These factors reduce environmental stress on the curing resin. In contrast, FDM prints are highly sensitive to drafts, temperature swings, and chamber design, which can drastically affect shrinkage behaviour. Therefore, SLA’s controlled environment ensures reduced 3D printing shrinkage, consistent curing and repeatable results.

No printing process is completely free of shrinkage. However, careful selection of low-shrinkage resins, proper temperature control, optimised support structures, and post-curing protocols can minimise it to acceptable levels.

Slow-curing or low-shrinkage oligomers will be the first thing to consider. Avoid designing large flat areas whenever possible, segment them, add fillets or lattice structures, and use adequate support structures. Proper slicing and controlled post-curing further reduce deformation.

Yes. SLA shrinkage is chemical rather than thermal, layer bonding is more uniform, supports reduced deformation, and the environment can be controlled.