Insulating unit are disclosed which are prepared by a cavity-filling, fast-gelling rigid polyurethane foam based on a formulation comprising a polyol component which contains at least 5 weight percent of an amine-initiated polyols and 1.4 to 4 parts by weight of a catalyst package whereby the catalyst package contains at least one amine catalyst and the weight percent nitrogen present in the amine-initiated polyol to weight percent nitrogen present in the catalyst system is from 2 to 8. The formulation is injected into the cavity and the pressure in the cavity is subjected to reduced atmospheric pressure to achieve the rigid foam having a thermal conductivity of less than about 19 mW/mK at 10°C average plate temperature.