Several processes now print flexible materials, and they behave less alike than their hardness numbers suggest. A printed elastomer's stiffness, its recovery after being compressed and its surface all differ by process, and the property that usually decides whether a part works is compression set rather than hardness, which almost no datasheet leads with.
The three routes
Filament printed thermoplastic polyurethane is the cheapest and most widely available, and gives genuinely tough parts with visible layer lines. Powder sintered elastomers give isotropic parts with a matte surface and no supports, at higher cost. Flexible photopolymers give the smoothest surfaces and the widest hardness range and are the least durable of the three.
Hardness is not the whole specification
Shore hardness says how far the surface indents and nothing about how the material recovers, how it behaves at temperature, or how it resists tearing. Two materials at the same hardness can feel similar and perform completely differently in a seal, a hinge or a bumper. Ask for tear strength, elongation and compression set, not just the Shore number.
Why printed seals disappoint
A seal works by being compressed and staying compressed, so compression set is the governing property, and printed elastomers generally have worse compression set than moulded ones. Layer lines also give leak paths on filament printed parts. A printed seal is a good way to check geometry and a poor way to check sealing, and moulded or cast silicone is the honest answer.
Designing for flexible printing
Thicker sections print more reliably in flexible materials than thin webs, which can be dragged by the nozzle. Avoid long unsupported spans on filament machines. For powder sintered elastomers, remember that no supports are needed, which opens up geometry the other processes cannot make. And test the actual function rather than inferring it from hardness.
Questions people ask about 3d printing elastomers
Can 3D printing make rubber parts?
It makes elastomeric parts in thermoplastic polyurethane, sintered elastomer powders and flexible photopolymers. None is vulcanised rubber or silicone, and the differences matter.
How does TPU print?
On filament machines, slowly and with careful extrusion settings because the material is flexible enough to buckle. Direct drive extruders handle it far better than remote ones.
Why does my printed seal leak?
Usually compression set and layer lines. Printed elastomers do not hold compression like moulded ones, and layer boundaries give a leak path. Cast or mould the seal instead.
What should I ask for besides hardness?
Tear strength, elongation at break and compression set, plus the temperature range. Hardness alone predicts feel and not performance.