3DPrintCalcs
Flexibility Calculator — Shore Hardness & Flex Properties
Calculate shore hardness and flex properties for TPU and flexible filaments.
How We Calculate This
Flexibility Calculations
- Effective stiffness = Base flex modulus x Infill factor
- Infill factor = 0.3 + (Infill% / 100) x Flex factor
- Deflection = Force x Length³ / (48 x Effective stiffness x Moment of inertia)
- Moment of inertia = Width x Thickness³ / 12
The deflection estimate treats the flat part as a simply-supported beam with a 1kg point load at its centre. Wall thickness affects only the moment of inertia (the section geometry), not the material modulus. Lower stiffness, thinner walls and a longer span all increase deflection (more flex).
This is small-deflection (Euler–Bernoulli) beam theory, which is only accurate while the bend stays small relative to the span. For very soft TPU the predicted deflection can exceed the part length — when it does, the figure is shown only as an indicative flex comparison, not an exact physical prediction.
Frequently Asked Questions
Shore hardness measures material flexibility on a scale. Shore A is for soft materials (rubber, TPU) where lower numbers = softer. Shore D is for harder materials. TPU 95A is the most common flexible filament — roughly as hard as a skateboard wheel or a rigid shoe heel. (A car tyre tread is softer, around Shore 70A, closer to TPU 85A.)
TPU 95A and harder (98A) can work on Bowden setups if you print very slowly (10-15mm/s), use a short Bowden tube, and disable retraction. Softer TPUs (85A, 90A) generally require a direct drive extruder.
Lower infill makes flexible prints even more flexible. 10-20% infill with 2 walls gives maximum flex. 100% infill makes TPU prints nearly solid and much stiffer. The infill pattern also matters — gyroid and grid flex more evenly than lines.
Print at 20-30mm/s, 220-240°C nozzle, 50°C bed, no retraction or minimal (0.5-1mm at 25mm/s). Disable Z-hop. Use direct drive if possible. Print with 2-3 walls and 10-20% infill for best flexibility.
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Last updated: February 2026
All calculations are estimates. Always verify settings with test prints before committing to final prints.