Developments in hydrogenated block copolymers promise to give sealants the balance between durability and conformability that they need. Could block copolymer sealants overcome their also-ran status in the marketplace? Despite being employed in adhesive compositions for many years block copolymers today possess a comparatively small share of the sealant market, at least in the US. The advantages offered by their high cohesive strengths and their ability to crosslink without a chemical vulcanization step are today overshadowed in this market by polyurethane, silicone, and even butyl rubber-based formulations. Yet, versatile adaptations of block copolymer chemistry could provide the ability to overturn this situation. As gap fillers, sealants are used in fairly thick layers in spaces between two substrates.2 Since the substrates frequently move relative to each other, sealants are usually low modulus compositions capable of withstanding this movement. From this viewpoint, and that of initial tack, the cohesive strength of block copolymers like styrene-butadiene-styrene (SBS) is a detrimental quality.