Silicone materials are well known to be one of the most suitable materials for optical and opto-electronic applications, such as LED encapsulants and lenses. Silicones have also been noted as an ideal material for the encapsulation of PV cells. This is primarily due to their high transparency in the UV-Visible wavelengths, wide range of refractive indices, excellent tolerance to high optical flux and excellent thermal and environmental stability. Silicones can be formulated to a refractive index between 1.38 and 1.58 depending upon the chemical constituents attached to the silicon atom. Due to their low modulus and low glass transition temperature (-50 °C) they are very stress relieving in a wide temperature range. Also, when formulated with appropriate adhesion, they provide the required moisture protection needed for multiple applications. They have very good electrical properties and are well known as dielectric insulators. In many applications, their fire resistant properties are also important. These properties make them ideal candidates as encapsulants for photovoltaic modules. Internal evaluations at Dow Corning and with select external partners have shown that very efficient solar cells using silicones as the encapsulant can be assembled and show very good reliability. This paper will focus on the key properties of silicones both initial and after aging. Also discussed will be performance measurements on PV cells encapsulated with Dow Corning® brand silicones. Long-term durability in outdoor applications has been demonstrated.