Balsa Density, Grain, and Grade

Written by Al and Rod Clark Learn about balsa, grades, densities, grains, and proper applications. Information and tips for any balsa kit, plans, or scratch build projectWhen you are tackling your next balsa project, spend a few moments to learn about the different densities, grades, and grains of balsa. Not all balsa is created equal and its application depends on the characteristics.

Balsa Density

GradeUltra LightLightLight MediumMediumMedium HardHard Density in
lb/cu.ft4-5.45.5-6.0 6.1-7.57.6-9.59.6-1214 + |----Contest Grade Balsa----||-------------Non Contest Grade Balsa-------------| So how do you determine the density and grade of balsa? It is a two step process to determine the various density ranges shown above. First, weigh the sheet of balsa. While there are very accurate electronic scales, I'd suggest you use a small postage scale (the kind with a weight and clip). Once you know the weight of the balsa refer to the nomographs below to determine the density.

Balsa Density Nomographs

After you weight a sheet of balsa the following nomographs are used to identify the balsa density and grade.

Balsa Grains

Builders should take note of the different balsa grains. Each grain type has different characteristics and should be used in different applications. Notice that the C-grain balsa sheet has a mottled appearance and distinct checkerboard pattern. It is very stiff across the sheet and splits easily. It will not easily wrap around curved surfaces without cracking. C-grain is used for sheet balsa wings and tails, flat fuselage sides, wing ribs, formers, and trailing edges. C-grain is usually hard to find in local hobby shops. I mainly use it for sheet tail surfaces. B-grain grain lines are shorter than A-grain and it is less stiff than C-grain. If you look at the narrow edge of the balsa sheet, B-grain will look the same as it does on the wide, flat side. B-grain can go around soft curves without cracking. This grain is used for flat fuselage sides, wing ribs, formers, planking gradual curves, and wing leading edge sheeting. A-grain has long fibers that show up as long grain lines. If you look at the narrow edge of the balsa sheet, A-grain will have a checkerboard appearance. This is the most flexible of all grains, and it is quite easy to wrap around curved surfaces. A-grain is typically used for sheet covering rounded fuselages and wing leading edges, planking fuselages, forming tubes, strong flexible spars, and hand launch glider fuselages. By Al and Rod Clark