Our insulation advice may seem counterintuitive. On energy-efficient radiant heat flooring, ignore all the standard sustainability advice about maximizing insulation R-values. You need more heat to come through the floor, so lower R-values are better. On the other hand, maximize sound insulation no matter the flooring or sub-floor. Wool and cork block both sound and heat, so they are not a great option for radiant heat applications, but highly recommended for other floors.
Don't forget to consider sustainability when choosing an underlay for floating floors. Cork, recycled rubber, and wool are among the many green flooring underlay options.