HDU density is one production variable in a routed sign. It describes the mass of the foam per cubic foot, but the best board still depends on detail, thickness, support, finish and the way the sign will be mounted.
What the density number actually describes
A 15-pound, 18-pound or 20-pound HDU designation refers to approximate pounds per cubic foot. It does not mean a full sheet weighs that number of pounds, and it does not by itself tell you how strong a finished sign will be.
Higher density gives a firmer material with more substance in the same volume. That can help with very fine relief or narrow routed details, but geometry and remaining material around the cut still matter.
15-pound HDU is our normal routed-sign starting point
For most exterior routed signs we begin with 15-pound HDU because it machines cleanly, takes primer and paint well and gives a practical balance of detail, weight and cost.
A well-designed 15-pound panel can carry deep texture, routed borders and dimensional copy when thickness and relief are planned together.
When 18- or 20-pound material makes sense
Denser boards can be useful for small intricate elements, narrow raised detail, unusually crisp relief or a written customer specification. The need should come from the design rather than from choosing the largest number on a data sheet.
If a project needs a denser grade, we identify that in the production scope before routing so material cost, machining and shipping are all based on the same specification.
Outdoor life depends on the complete sign system
Density does not replace proper preparation, coating, drainage, backing or mounting. An excellent board with poor paint preparation or bad attachment can still produce a poor exterior sign.
We evaluate the routed panel as a system: substrate, remaining thickness, relief depth, primer, topcoat, hardware, exposure and how the installer will support it.
How to specify HDU density on a routed-sign quote
If a plan, municipality or end customer requires a particular density, put that requirement in writing with the artwork and dimensions. If not, describe the finished sign and let the fabrication requirement drive the board selection.
RoutedSignage.com normally assumes 15-pound exterior-grade HDU for routed work unless the quote or approved drawing identifies another material or density.
Frequently asked questions
Is 20-pound HDU automatically better than 15-pound?
No. It is denser, but the useful choice depends on the design, routed detail, thickness and support.
Does higher-density HDU last longer outdoors?
Not by itself. Coating, drainage, hardware, installation and exposure have major effects on service life.
What density do you normally use?
We normally begin with 15-pound exterior-grade HDU for routed signs unless the project gives us a reason to specify something else.
Can 15-pound HDU hold detailed routing?
Yes, for many designs. Very fine or fragile features still need sensible geometry and enough material around the cut.
Does density change sign weight?
Yes. A denser board contains more material in the same volume, so otherwise identical parts are heavier.
Should my drawing call out density?
Only when it is a real project requirement. Otherwise dimensions, relief, finish and application are more useful starting information.