Epoxy: generally, epoxy offers high temperature and chemical resistance as well as better adhesion. Epoxies also usually don’t need primers and can adhere to various kinds of substrates. Moreover, they also provide higher tensile strength and modulus. If you are specifically looking for an electrical potting compound that is an outstanding option for outdoor application, then go for an epoxy because it has an excellent moisture resistance. And lastly, this potting material has great dielectric properties, making it the ultimate choice for potting transformers and switches.
Urethane: this compound is a perfect option if you require high abrasion resistance and flexibility. It specifically works great in devices where large stresses will be encountered due to a mismatch in component composition. Most of urethane materials offer extremely low glass transition temperatures, making them ideal to use in consumer electronics. In addition, they can be designed and formulated to work in a wide array of physical properties, as well as react to room temperature with the aid of catalysts and isocyanates.
Silicone: of all three potting compounds, silicone offers the widest operating temperatures. A specially formulated silicone electrical potting compound can work even at below -100°C and can handle as high as 200°C. With their low modulus, silicone materials provide the least amount of stress at these temperature ranges.