We characterize a recently discovered material that forms an ultra-hermetic environmental barrier layer for the protection of organic light-emitting displays. The layer is deposited by plasma-enhanced chemical vapor deposition (PE-CVD) from the nontoxic precursor gases, hexamethyl disiloxane and oxygen. We measured the PE-CVD deposition rate, wet and dry etch rates, IR absorption spectrum, wetting contact angle with water, surface roughness and phase shift from atomic force microscopy, coefficient of thermal expansion, elastic modulus, critical tensile strain, indentation hardness, optical absorption spectrum, refractive index, relative dielectric constant, and electrical conduction, many over a range of PE-CVD conditions. The properties reflect a continuous transition from those of plasma-polymerized silicon to those of silicon dioxide prepared by thermal oxidation of silicon. In addition to low permeability, the critical strain, fracture toughness, thermal expansion coefficient, optical transmittance, and refractive index have values that are desirable in a hermetic encapsulant for organic light-emitting displays.