Which Is Stronger and Why: Plexiglass or Glass?

Tensile Strength

• Tensile strength is the measure of the force required to pull a material apart. The tensile strength of plexiglass can be as much as 11,000 pounds per square inch, or psi, which allows plexiglass to stretch imperceptibly under stress before breaking. Glass, on the other hand is relatively brittle due to its non-crystalline properties. Non-crystalline molecules don't contain sheets of atoms like crystals, which can slip past each other to relieve stress and prevent sudden shattering. Glass is also susceptible to tiny fractures, and breakage usually occurs along these fractures.

Compressive Strength

• Compressive strength is the measure of a material’s ability to resist forces trying to squeeze or compact the material together. The compressive strength of plexiglass is 18,000 psi, or 124 mega pascals, or MPa, while glass’s compressive strength is 5,802 psi, or 40 MPa. The difference is counterintuitive, because glass seems harder and less compressible, but plexiglass is stronger because its polymeric, which refers to a long molecule composition that resists compression better than glass’s non-crystalline structure.

Flexural Strength

• Flexural strength is the measure of a substance’s ability to resist breakage from bending--in other words, flexibility. Plexiglass’s flexural strength is between 14,000 and 17,000 psi, or 100 to 117 MPa. Different glass types have varying characteristics, depending on the method of manufacture and materials added during manufacture. In general, though, the flexural strength of glass is lower than that of plexiglass.

Modulus of Elasticity

• Modulus of elasticity, also called Young’s Modulus, is the measure of the force required to produce change in dimension--in other words, stiffness or rigidity. A high modulus indicates rigidity, or the material's ability to hold its shape under a load. Plexiglass’s modulus is 450,000 psi, or 3,103 MPa, while the modulus of elasticity of glass is 10,000,000 psi, or 70,000 MPa.