Astragal Materials, Sizes, Shapes and Colors – Getting to the Bottom of It

Astragal, it’s a funny word. When it comes to garage doors, astragal is the technical term for a bottom seal on a garage door. Bottom seals come in many different materials, sizes, shapes and colors based on the requirements of the application.

Starting with materials, flexible PVC (Polyvinyl Chloride) is the most common material used for bottom seals. Followed by materials in the rubber family, in most cases EPDM (Ethylene Propylene Diene Monomer). There are other, less common materials, that fall between the properties of flexible PVC and EPDM.

One of the big reasons for the different materials is to allow a seal to remain pliable and function as needed in a wide range of temperatures. Flexible PVC has a functional temperature range of -30 to 140 degrees Fahrenheit. EPDM is best in temperatures from -60 to over 200 degrees Fahrenheit.

When it comes to the size of the seal, door thickness and the floor surface that the seal comes into contact with has a bearing on what size of seal to use. For a typical “U” shaped seal, size of the seal is measured with the seal lying flat. “U” Shaped seal sizes range from roughly 3 inch to 6 inch or even larger for specialty applications. The need for different sized seals is due to how the seal protrudes from the bottom of the door when installed. If the seal is installed on a door that is 1 3/8″ thick it could use a smaller seal, while a thicker door typically needs a larger seal. The next factor in seal size has to do with the surface it is sealing against. Most newer garage floors are quite flat and don’t have a need for a large seal to seal the gap between the bottom of the door and the floor. Older floors that have more irregularities in the surface can benefit from a door with a larger seal that will protrude further from the door and create a larger sealing footprint when the door is closed.

Within the family of “U” shaped seals, at the ends of the seal there are profiles that mate with the retainer on the bottom of the door. These may be “T” shaped, Round Beads or 1/2 “T” shaped that go into a single retaining slot just to name a few.

Besides “U” shaped seals, which are the most common, there are other shapes that are specific to particular doors. Even if a seal isn’t available for your specific door bottom design there are ways to adapt the bottom of the door to accept a readily available seal.

When it comes to color, for the most part, flexible PVC seals will either be black or gray, but the process of making flexible PVC allows for an almost endless color pallet. There are applications that have a need for yellow seals to highlight the bottom of a door for safety compliance and that is typically a flexible PVC material. EPDM seals are almost always black since that is the most common color for EPDM in the rubber industry.

If you have questions about what astragal will be right for your application contact your local Action Industries dealer to determine the right seal for your application.