Resin Types Compared: Standard, Engineering, Flexible, and Castable

Resin formulations vary as widely as FDM filaments, and the categories have distinct properties that match very different applications. Using standard resin for a functional part that needs to withstand impact is as mismatched as using PLA for an outdoor structural bracket.

Standard Resin

Standard resin produces the highest surface quality and finest detail resolution of the common resin types. It is optimised for appearance rather than mechanical performance — parts are relatively brittle and will crack rather than flex under load.

Best for: Visual prototypes, display models, jewellery prototypes, architectural detail models, dental and medical visual models, miniatures and figurines.

Not suitable for: Functional parts subject to impact, flexing, or mechanical stress.

Surface finish is the primary strength — standard resin straight off a well-calibrated printer requires minimal sanding to achieve a smooth, paint-ready surface.

Tough / Engineering Resin

Tough resins use a modified polymer chemistry to produce parts with significantly better impact resistance and reduced brittleness compared to standard resin, while retaining good surface detail. The trade-off is slightly reduced maximum surface smoothness and higher cost.

Best for: Functional prototypes that will be tested, snap-fit connectors, parts subject to repeated assembly and disassembly, jigs and fixtures that need to handle mechanical contact, end-use parts in lower-stress applications.

Examples: Monocure 3D Tough series, Phrozen ABS-Like, most engineering-grade resin formulations.

Flexible Resin

Flexible resins produce rubber-like parts that can be compressed and bent without cracking. Shore hardness typically ranges from 50A to 80A depending on the formulation — softer than most TPU FDM filaments. Detail resolution is slightly reduced compared to standard resin.

Best for: Gaskets and seals for complex geometries, vibration dampers, grip surfaces, articulated joints, any application requiring compression and recovery.

Note: Flexible resin parts are more difficult to support and handle during printing. They are more prone to tearing during support removal. Design parts to minimise the number of supports contacting flexible surfaces.

Castable Resin

Castable resins are formulated to burn out cleanly from an investment casting mould without leaving ash residue that contaminates the metal. The printed part is embedded in investment plaster, the resin burns out in a kiln, and molten metal is cast into the void.

Best for: Jewellery in precious metals, small metal components where the geometry would be impossible to machine, custom hardware in aluminium or bronze.

Process note: Castable resin burn-out requires specific kiln cycles — the resin must reach sufficient temperature for complete combustion. Standard ceramic investment and the correct kiln schedule are as important as the resin itself for quality casting results.

Quick Selection Table