Dual durometer rubber products are extrusions with different areas of hardness. Typically, the harder rubber is used for attachment while the softer rubber is used for sealing. Sometimes, different materials are used because of design considerations such product color schemes or the use of pressure-sensitive adhesives (PSAs).
By fabricating dual durometer rubber into a single part, a product such as window seal can have areas with different physical properties to meet application requirements. With window channels, the harder window rubber attaches to the window frame and the softer window rubber faces the glass window. Durometer is not limited to window seals, however, and is used with both sponge and solid profiles.
Dual Durometer Rubber: Sponge and Solid
Sponge rubber can be shaped into various industrial rubber products, including dual durometer profiles. By combining sponge rubber and solid rubber into a single part (such as bulb trim seals), different areas of hardness are achieved. Typically, sponge profiles are characterized as soft, medium, and firm. Sponge rubber can be open cell or closed cell.
Solid rubber is harder than sponge rubber and, therefore, most resistant to compression. Most solid profiles range from under 30 duro to over 120 duro, depending on their shape. At 40 duro, solid rubber profiles have the consistency of pencil erasers. At 90 duro, they are hard like hockey pucks. Under low temperature conditions, solid profiles become harder.
Dual Durometer Materials and Specifications
Standard dual durometer products such as bulb seals are often made of EPDM or TPE. A type of synthetic rubber, EPDM provides insulation against hot and cold temperatures. Thermoplastic elastomers (TPE) are rubber-like materials that combine the processing strengths of thermoplastics with the best qualities of thermoset rubbers.
When choosing standard dual durometer seals, consider product specifications such as materials, applications, seal dimensions, quantity per box, and quantity per coil. Tooling costs are higher for custom, complex parts; however, a wide range of standard, in-stock dual durometer profiles are available.