18 Jun What exactly is sign foam?
Many of our signs, especially our sand blasted signs, are made of sign foam, or High-density urethane. But what is HDU?
High-density urethane foam was invented specifically for the sign industry as a durable alternative to wooden outdoor signs. HDU is considered a “closed cell” foam that contains more solid urethane and less air than traditional foam products, like Styrofoam cups, making it much stronger, waterproof and able to withstand the elements. The urethane base also means that it can’t be destroyed by any petroleum-based solvents, making it a cost-effective solution for three-dimensional outdoor signs.
HDU vs. Wood
HDU never warps, splits or rots, and it isn’t susceptible to the same natural variations as wood. Wood planks for signs are laminated together and contain unpredictable weak spots, which can cause damage when the wood expands and contracts with temperature and water exposure. HDU is manufactured into uniform sheets that come with a guarantee unavailable with wooden signs. The material is made at specific weights and sizes and can be sandblasted and painted in any way you need.
HDU foam specifications are measured using the American Society for Testing and Materials standard tests for compressive, flexural, tensile and shear strength, and modulus. HDU comes in 10-, 15- and 18-lb. densities that are tested under the same conditions to produce uniform specifications, so you can compare the differences in each weight and purchase the one that best fits your needs. The benefit of using standard ASTM specifications for HDU foam is that the properties won’t vary by manufacturer.
(information from ehow/info_8778843_high-denisty-urethane-sign-specifications.html)