Gasketing

Polyurethane VS. Silicone

SLP robots dispense a liquid gasket directly inside a light fixture’s housing. We offer two dedicated gasketing systems, polyurethane and silicone. Both result in a reliable seal that prevents dust, moisture, and contamination. The differences between polyurethane and silicone are outlined below.

Polyurethane gasket bead dispensed inside a fixture housing
PU ~10%+
Compression Set
lower is better
SI <5%
PU Higher
Clamping Force to Seal
lower is better
SI Lower
PU -40° to 194°F
Temperature Range
wider is better
SI -67° to 450°F
PU Good
UV / Ozone Resistance
higher is better
SI Excellent
PU Lower
Relative Cost
lower is better
SI Higher
Silicone gasket bead dispensed inside a fixture housing
Polyurethane
Hydrogen Oxygen Carbon Nitrogen Silicon
Silicone
Polyurethane
Urethane linkage (–NH–CO–O–)
Polyurethane urethane linkage molecular structure
SLP robotic equipment dispensing liquid gasket into fixture housings
Robotic pour-in-place dispensing
Silicone
Siloxane (Si–O) backbone
Silicone siloxane Si-O backbone molecular structure

Choosing the Seal

For vapor-tight housings, the deciding factor is compression set. It’s the amount of thickness the gasket loses for good after being clamped down. Lower is better. A gasket that springs back keeps sealed; one that remains smashed leaves a path for water.

Silicone wins here. Silicone foam holds compression set under 5%, against roughly 10% for polyurethane foams. That means silicone seals with less clamping force, keeping water out without a tight, forceful squeeze. The seal protects inside electrical components and holds through years of thermal cycling.