What is Shore hardness?

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.)

Can I print TPU on a Bowden printer?

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.

How does infill affect flexibility?

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.

What print settings work best for TPU?

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.

3DPrintCalcs

Flexibility Calculator — Shore Hardness & Flex Properties

Calculate shore hardness and flex properties for TPU and flexible filaments.

MaterialLower Shore A = softer/more flexible; PETG and Nylon are rigid references

Infill

Infill density — lower (10–20%) gives a more flexible part; 100% is much stiffer

Wall Thickness

Total thickness of outer walls

Part Width

Cross-section width of the flat part (across the load)

Part Length

Unsupported span that bends under load

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

Related Calculators

PLA vs PETG Calculator

Compare PLA and PETG properties side by side for your specific use case.

Material Strength Calculator

Estimate tensile and compressive strength based on material and print orientation.

Heat Resistance Calculator

Check if your printed part will withstand a given operating temperature.

Material Weight Calculator

Calculate the weight of a printed part from its volume and material density.

Post-Processing Calculator

Estimate time and materials for sanding, priming and painting printed parts.

Last updated: February 2026

All calculations are estimates. Always verify settings with test prints before committing to final prints.