How stiff is balsa wood? Young's modulus explained
What stiffness (Young's modulus) means, typical balsa values of about 2 to 4.5 GPa, and why stiffness decides when a long stick buckles.
Updated · 1 min read
Short answer: stiffness (Young's modulus) measures how much a material stretches or shortens under a given stress. For hobby balsa at about 150 kg/m³ along the grain, our planning estimate is about 3.5 GPa, with a plausible range of about 2.0 to 4.5 GPa.
Strength and stiffness are different
- Strength is how much stress a material takes before it breaks.
- Stiffness is how little it deforms under stress.
A stick can be strong but bendy. For a pushed stick, stiffness matters most, because buckling load rises in direct proportion to stiffness. See preventing buckling.
Values from tests
Axial tests of balsa along the grain generally give about 3 to 4 GPa near 150 kg/m³. Values from bending a stick are lower, about 2 GPa, because bending tests include extra deflection from shear, and tiny hobby sticks are hard to clamp rigidly. Across the grain, balsa is far more flexible, with moduli of order tens to a couple of hundred MPa.
Stiffness rises with density, roughly as density to the power of 1.4, so a denser stick is disproportionately stiffer.
What to do with it
Use your stiffest, densest sticks for pushed members. See choosing sticks. These numbers are estimates from published tests and vary a lot between sticks. See how strong balsa is.