Devices suitable for implantation in a body of a host and systems and methods for their manufacture are provided. The implantable devices include a composite material formed at least from a matrix material and hollow gas-filled beads. In preferred embodiments, the composite material includes a polymeric matrix mixed with hollow air-filled glass beads, which are mixed and cured to form at least a portion of the body of the implantable device. Implantable devices including this composite material have decreased weight and/or overall density as compared to implantable devices without the beads incorporated therein, which is believed to improve the acceptance and function of the implantable device in vivo. Additionally, implantable devices concerned with transmitting and receiving via RF are believed to achieve improved RF performance due to a reduced dielectric constant provided by the incorporation of beads within the composite material.