electrical enclosure metal box, emi gasket spot

When customers look for high-performance conductive elastomer gaskets, two of the most commonly requested materials are CHO-SEAL 1285 and CHO-SEAL 1287. Both materials use silver-plated aluminum (Ag/Al) as the conductive filler — but they differ in one critical way:

Cho-Seal 1285 uses a silicone rubber binder.
Cho-Seal 1287 uses a fluorosilicone rubber binder.

That single change drives most of the performance differences between the two.

Below is a clear breakdown.

CHO-SEAL 1285 – Silver-Aluminum in Silicone

Equivalent MIL classification:

• CHO-SEAL 1285-40 → MIL-DTL-83528 Type B

What It Is

CHO-SEAL 1285 is a 65 durometer silicone-based silver-aluminum conductive elastomer. Silicone provides broad temperature performance, good compression set, and strong EMI shielding — all at a lower cost than fluorosilicone options.

Where It’s Used

• General EMI & environmental sealing

• Indoor electronics

• Ground vehicles

• Housings with moderate environmental exposure

• Applications where fuel/solvent resistance is NOT required

Why Customers Choose It

• Excellent shielding (Ag/Al filler)

• Strong corrosion resistance

• Excellent general-purpose performance

• More economical than fluorosilicone-based materials

• Meets MIL-DTL-83528 Type B when specified as 1285-40

• Sheet Sizes, 40-10-1020-1285 (.020”), 40-20-1020-1285 (.032”), 40-30-1020-1285 (.062”), 40-40-1020-1285 (.094”), 40-50-1020-1285 (.125”), 40-60-1020-1285 (.045”)
• NEDC stocks this material in 10” x 20” sheets for purchase from any consumer.

CHO-SEAL 1287 – Silver-Aluminum in Fluorosilicone

Equivalent MIL classification:

• CHO-SEAL 1287-40 → MIL-DTL-83528 Type D

What It Is

CHO-SEAL 1287 is a 70 durometer,  fluorosilicone version of Ag/Al conductive elastomer. The filler is identical to 1285 — but the binder chemistry is completely different.

Fluorosilicone is the material of choice for environments involving:

• Fuels

• Hydraulic fluids

• Oils

• Solvents

• Salt fog / marine exposure

• Aircraft & aerospace conditions

Where It’s Used

• Aerospace avionics

• Defense electronics

• Marine environments

• Any assembly exposed to JP-8, Jet-A, Skydrol, oils, or aggressive chemical contact

• High-reliability EMI sealing in ruggedized housings

Why Customers Choose It

• Dramatically superior chemical resistance

• Long-term stability in harsh environments

• Excellent EMI performance similar to 1285

• Meets MIL-DTL-83528 Type D when specified as 1287-40

• Sheet Sizes, 40-10-1020-1287 (.020”), 40-20-1020-1287 (.032”), 40-30-1020-1287 (.062”), 40-40-1020-1287 (.094”), 40-50-1020-1287 (.125”), 40-60-1020-1287 (.045”)
• NEDC stocks Cho-Seal 1287 in 10” x 20” sheets for purchase by any consumer.

The Difference in One Line

1285-40 = MIL-DTL-83528 Type B (silicone).
1287-40 = MIL-DTL-83528 Type D (fluorosilicone).

Both use the same silver-aluminum filler.
Both offer high-level EMI shielding.
But binder chemistry determines survivability. The -40 suffix indicates its for MIL-DTL-83528 certified.

Side-by-Side Comparison

NEDC’s Capabilities with These Materials

NEDC converts both CHO-SEAL materials into:

• Precision die-cut gaskets (a lot of EMI Connector Gaskets) 

• Extruded profiles & cut lengths

• Spliced O-rings

• Adhesive-backed EMI gaskets

• Custom shapes & designs

Each application is reviewed for:

• Compression requirements

• Flange design

• Environmental conditions

• Shielding targets

• Material compatibility