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Elasto Proxy's Sealing Solutions Blog Blog

Elasto Proxy's Sealing Solutions Blog

Elasto Proxy's Sealing Solutions Blog is the place for conversation and discussion about the design and custom fabrication of rubber and plastic components. For nearly 25 years, our family-owned company has provided high-quality, low-volume seals to a variety of industries. Doug Sharpe, Elasto Proxy's co-founder, is a former president of the International Sealing Distribution Association (ISD), a not-for-profit trade association that enhances member success through information, education, and interaction. By blogging for CR4 in this same supportive and collaborative spirit, Doug and other members of the Elasto Proxy team will share our experiences with you.

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Bulb Trim Seals: Compounds, Colors, and Approvals

Posted December 18, 2017 10:10 AM by Doug Sharpe

Bulb trim seals don’t just come in EPDM rubber. They’re available in colors besides black, too. That’s good news if you need to use recyclable materials, or if you’re searching for colorful sealing solutions to complement distinctive product designs. Bulb trim seals that contain EPDM aren’t all the same either. Some meet specific industry or regulatory standards. Others are made of harder or softer rubber.

Do you need bulb trim seals for doors, hatches, or enclosures? In this week’s blog entry, Elasto Proxy’s last for 2017, we’ll finish the year with a flourish – and with a look at some of the compounds, colors, and approvals for bulb trim seals. Black EPDM gaskets are available if you need them, but procurement and engineering personnel may have more choices in compounds than they may realize.

Bulb Trim Compounds

As last week’s blog entry explained, bulb trim seals have separate bulb and retainer sections. The bulb compresses to form a seal when the door, hatch, or enclosure is closed. The trim or retainer section attaches to the flange or substrate. These sections can be made of the same or different materials, but typically have different durometers since the bulb needs to support compression.

Typically, the bulb section is made of EPDM, TPE, or silicone.

EPDM bulb trim seals provide excellent resistance to water, weather, ozone, aging, and steam. They also resist tearing, abrasion, and a range of outdoor temperatures. EPDM rubber doesn’t resist fuels and oils, and it’s not recyclable like thermoplastic elastomers (TPEs). Yet for applications like the door seals on mobile equipment, EPDM bulb trim seals are often the right choice.

TPE bulb trim seals cost more than EPDM, but thermoplastic elastomers (TPEs) are recyclable. That’s important for sustainability, or if you need to comply with the Restriction of Hazardous Substances (RoHS) directive. TPE profiles also have significantly tighter tolerances (2x) that most extruders can achieve with EPDM. TPE bulb trim seals are available in novel colors, too.

Silicone bulb trim seals are used in applications that require low toxicity, low chemical reactivity, and thermal stability over a wide temperature range. Silicone seals also repel water and resist oxygen, ozone, and ultraviolet (UV) light. Many different silicone compounds are available, but bulb trim seals that are made from these synthetic elastomers provide electrical insulation and won’t support microbial growth.

Some bulb trim seals contain a trim or retainer section that’s made of polyvinyl chloride (PVC), a smooth plastic that resists kinking and provides other desirable properties. For example, PVC is flexible and resistant to fracture. It’s also strong, lightweight, difficult to ignite, and resistant to abrasion. The trim section of a bulb trim seal can also include internal metal clips for improved gripping, too.


Most industrial rubber products are black, but bulb trim seals can come in other colors. This is especially important in industries (such as mobile equipment) where companies use distinctive colors to support larger product designs. Colors for bulb trim seals include black, white, off-white, beige, tan, gray, and silver. In the case of TPE bulb trim seals, profiles with translucent and metallic colors are available. Most bulb trim seals are smooth, but some have coarse, pebbled, or ribbed finishes.


Finally, the compounds that are used with bulb trim seals can meet specific regulatory requirements and industry approvals. Examples include:

  • FVMSS 302 for interior automotive parts
  • FAA/FAR 23.853 for aircraft interiors
  • UL 50E for electrical equipment
  • UL 94 HB for flame-resistance plastic parts
  • FDA standards for food contact and medical applications

In the mass transit industry, engineers and buyers can source Certified Transit Grade (CTG) bulb trim seals from Elasto Proxy that provide resistance to flame, smoke, and toxicity, (FST).

Find Bulb Trim Seals in 2018

We hope you’ve enjoyed this article from Elasto Proxy and wish you a happy holiday seasons. This is our final article for 2017, but we invite you to contact us if you’d like more information about bulb trim seals or other industrial rubber products. See you in 2018!


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Previous in Blog: Bulb Trim Seals: Three Measurements You Need to Know   Next in Blog: The Top 7 Sealing and Insulation Posts of 2017