An insulated spa cover (10) contains a thermal insulating core (30), a top cover (150) with an average permeance of at least 57.2 nanograms/Pascal*seconds*square meters, and a hydrostatic head test value of at least 5,000 Pascals, a vapor barrier (130) and optionally a bottom sheet (140) apart from the vapor barrier. Venting pathways are defined around the thermally insulating core to facilitate escape of water vapor.