The theory of homogeneous isentropic compression is extended to the case of hollow shells, and exact results for the growth of Rayleigh-Taylor instability during such compressions are obtained. Earlier results on the optical power PL required to achieve a given measure of inertial confinement ρR of a laser-driven isentropically-compressed DT pellet are extended to include the case of hollow shells. – It is found that a five-fold reduction in peak power should be attainable by imploding a hollow shell having an unablated-wall thickness equal to 10% of its radius, instead of a solid pellet. Further reductions in wall-thickness and peak optical power appear to be strongly limited by Rayleigh-Taylor instability.