Active implantable medical devices such as cardiac pacemakers are required to work in harsh physiological environments and must be protected in order to prevent device failure. Currently, hermetic packages are constructed using laser welded titanium cases and ceramic feedthroughs. As technology advances and medical devices shrink, the creation of hermetic packages becomes more difficult in smaller devices. Polyisobutylene (PIB) is a commercially important polymer due to its excellent thermal stability and excellent flexibility at ambient temperature. Many properties have been identified which differentiate PIB from other polymers, a key one being low penetrability to small molecules. A formulation of polyisobutylene diol has been developed by an industrial partner. This diol was developed in order to create a polyisobutylene polyurethane (PIB-PUR), a synthetic rubber anticipated to have low permeability to small molecules and be flexible at ambient temperatures. A means by which PIB-PUR samples can be fabricated in a laboratory setting was developed. The PIB-PUR samples were seen to exhibit ultimate tensile strengths in the range of 7.66–10.17 MPa and tensile failure strains in the range of 1148-1488%. PIB-PUR samples exhibited the Mullins effect. The water vapour transmission rate was examined for PIB-PUR and seen to be in the range of 0.03-0.04 g.cm/m2.day. Moisture absorption rates were also examined for both H20 and PBS solution for a period of 70 days and seen to be in the range of 0.79-2.24% and 0.57–1.38% respectively. The effect of incorporating polysorbate Tween 20 was examined and did not significantly affect the mechanical and permeability properties of PIB-PUR samples. There was no significant deterioration of mechanical properties over periods of up to 70 days in PBS solution at 37°C. Finally, the research findings are discussed with respect to the potential of this PIB-PUR material as a suitable candidate to be a near hermetic barrier for encapsulation of implantable electronic devices.