Elasto Proxy sources UL 94 HB rubber and fabricates flame retardant gaskets for data centers. The EPDM rubber that we use (EP-60020-FR) is UL Listed and has a UL Yellow Card, both of which are available as PDF downloads via our website. A confirmation letter that describes our participation in the UL Product iQ platform from Underwriters Laboratories (UL) is also available. Contact Elasto Proxy for UL 94 HB gaskets, or keep reading to learn more about these materials and our manufacturing capabilities.

What is UL 94 HB?

UL 94 HB is a flammability standard from Underwriters Laboratories (UL) that defines a horizontal burn (HB) test for a specimen that needs to resist electrical and electronic combustion. It is part of the larger UL 94 flammability standard for plastic materials and accounts for both the burn rate and a specimen’s thickness. UL 94 HB testing is performed with a 20 mm high burner flame for a total of 30 seconds. Prior to testing, the material is kept for 48 hours at 23° C (73.4° F).

The table below lists the test criteria.

Test specimen thickness 3 to 13 mm

≤ 40 mm/min

Test specimen thickness < 3 mm

≤ 75 mm/min

Flame is extinguished before first mark

= 0 mm/min

Why use UL 94 HB EPDM rubber for gaskets?

UL 94 HB EPDM rubber combines proven UL flame resistance with the strong environmental resistance of an ethylene propylene diene monomer (EPDM) elastomer.  Although standard EPDM gaskets have poor flame resistance, UL 94 HB EPDM gaskets can resist the spread of fire and are self-extinguishing. EPDM rubber is also electrically insulating and provides good strength, excellent heat resistance, and has a typical working temperature range from -50°F to +300°F (-45°C to 150°C).   

What are the key properties for this flame retardant material?

As listed on the UL Yellow Card, Elasto Proxy’s UL 94 HB EPDM rubber (EP-60020-FR) has the following flammability, ISO/IEC flammability, and thermal properties.



Test Method

Flammability Properties



(5.7 mm, Color: BK)



ISO/IEC Flammability Properties


IEC 60695-11-10


(5.7 mm, Color: BK)



Thermal Properties


Relative Thermal Index – Electrical Strength

(5.7 mm)

50° C (122° F)

UL 746B

Relative Thermal Index – Mechanical Impact

(5.7 mm)

50° C (122° F)

UL 746B

Relative Thermal Index – Mechanical Strength

(5.7 mm)

50° C (122° F)

UL 746B

Why do data centers need UL 94 HB gaskets?

Data centers are specialized facilities or locations within facilities that house computer, data storage, or telecommunications systems. They centralize an organization’s information technology (IT) operations, often for critical functions. The hardware in a data center contains electrical and electronic components and includes servers, switches, and routers that are housed in racks, some of which have doors. UL 94 HB rubber can be fabricated into flame retardant door gaskets or used to provide sealing and insulation for the data center’s HVAC system, which must function reliably because electronics generate heat.

How are UL 94 HB flame retardant gaskets made?

Elasto Proxy sources UL 94 HB rubber in sheets or coupons and then converts these materials into finished gaskets. To provide you with low-to-medium volume quantities, we use water jet cutting to make fast, clean cuts without costly metal tooling. At our manufacturing center near Montreal, Canada, we also provide services such as gasket bonding, parts marking, kitting, and custom packaging. Elasto Proxy can store the UL 94 HB rubber that you buy in our warehouses and use your sales forecasts to meet demand.    

What’s the best way to buy UL 94 HB gasketing?  

Contact Elasto Proxy to learn more about our flame rated rubber materials and to request a quote for UL 94 HB gaskets.

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