Flexural modulus

What it means in practice

Flexural modulus tells you how stiff a material is when it is bent. Our hub lists it as “bending modulus”. A higher value means a part deflects less under the same load.

Because most parts are loaded in bending, this is often the most practical stiffness number on a datasheet. It decides how much:

• A cantilevered bracket or arm droops under weight.
• An enclosure lid or wall gives when pressed.
• A jig or fixture moves when a part is clamped into it.
• A snap-fit arm resists being pushed open (stiffer arms need more force, and may crack if over-bent).

How it’s measured

It comes from the same three-point bending test as flexural strength. A bar rests on two supports and is pressed in the middle. The modulus is calculated from the slope of the load-deflection curve at the start of the test, before the material begins to yield.

• Standards: ISO 178 and ASTM D790.
• Units: MPa or GPa (1 GPa = 1,000 MPa). Watch for unit slips when a value looks a thousand times too small or too large.

How to read and compare it

• Close to, but not the same as, tensile modulus. For unfilled plastics the two are often similar. For printed parts and fibre-filled materials they can differ, because bending loads the outer skin most.
• The skin matters. In a printed part, outer walls carry most of the bending stress. Wall count and top/bottom layers change real-world stiffness as much as the material does.
• Orientation. Fibre-filled filaments are stiffest along the print direction. A sheet that does not say how the bar was printed is hard to compare. See print orientation: XY vs Z.
• Heat and time. Stiffness falls as temperature rises and under long-term load (creep). Room-temperature values are a starting point only.
• Same standard, same conditions. Compare ISO with ISO and ASTM with ASTM where you can. See ASTM vs ISO.

Range in our catalog

• Standard materials: 575–3,800 MPa (median 2,191 MPa, 62 materials)
• Resins: 570–11,965 MPa (median 2,200 MPa, 130 materials)
• PLA filaments: 1,860–6,320 MPa (median 2,823 MPa, 25 materials)
• Carbon-fibre filled: 2,887–53,300 MPa (median 5,596 MPa, 44 materials)
• Glass-fibre filled: 2,400–22,000 MPa (median 4,557 MPa, 24 materials)

1. PLA 241,860–6,320
2. PETG 141,068–5,740
3. ABS 17856–5,260
4. ASA 71,733–5,210
5. PC 122,050–6,540
6. PA6 92,050–7,038
7. PEI 122,170–8,560
8. PEEK 102,400–11,200

Bar = lowest to highest, dot = median. 105 materials, live from our database.

Highest and lowest in our catalog

Stiffest in bending

Stiffest resins

Least stiff flexible materials

Related properties

• Young’s modulus — stiffness under a straight pull.
• Flexural strength — the bending load at failure.
• Heat deflection temperature — where bending stiffness gives way to heat.
• Density — for stiffness-to-weight comparisons.

Find stiff materials in the finder