Discussion of selected wood species bending strengths and stiffness.
Ultimate bending stresses (psi) and Modulus of Elasticity (stiffness)
Results of tests on small, clear straight-grained specimens @ 12% moisture content, Source: Wood Handbook, Wood as an Engineering Material, US Dept. of Agriculture:
| bending strength | modulus of elasticity | |
| Basswood, American* | 8700 | 1,460,000 |
| Cedar: | ||
| Alaska | 11,100 | 1,420,000 |
| Atlantic White | 6,800 | 930,000 |
| Eastern Red | 8,800 | 880,000 |
| Incense | 8,000 | 1,040,000 |
| Norhern White | 6,500 | 800,000 |
| Port Orford | 12,700 | 1,700,000 |
| Wester Red * | 7,500 | 1,100,000 |
| Spruce | ||
| Black | 10,300 | 1,530,000 |
| Englemann* | 9,300 | 1,300,000 |
| Red | 10,200 | 1,520,000 |
| Sitka | 10,200 | 1,570,000 |
| White | 9,800 | 1,340,000 |
* denotes used by Clark Faom
Discussion of relative bending strengths increases at selected thicknesses:
Bending strengths are a direct function of the thickness of a material. The strength increases in proportion to the square of the thickness of the material.
Therefore, the relative strength increases for the following thickness (2 ¾" as the base):
| Thickness | Thickness Increase | Relative Strength Increase |
| (from 2.75") | (from 2.75") | |
| 2.75" | ||
| 3" | 9% | 19% |
| 3.125" | 9.75% | 29% |
| 3.25" | 10.5% | 39% |
| 3.5" | 12.25% | 62% |
| 3.75" | 36.3% | 85% |
Discussion of elasticity (flex) of woods
A surfboard is basically two surfaces of fiberglass separated by a foam core, otherwise known as "foam sandwich construction". The more a board will flex, the more likely the fiberglass will "buckle", and lose its strength. Once this occurs, the board begins to break. Thus, the stiffer the board (caused by stiffer woods and higher density core foam), the less likely it is to break Basswood, as shown by the chart, is one of the least flexible woods, and also has a high bending strength. Western Red Cedar has the lowest combined strength of the woods used by Clark Foam (and others).