Residential insulation in Michigan is studied from the user's point of view. From surveys and from open-ended ethnographic interviews, we analyze who is adding insulation, how they decided to do so, and what financial savings they expected. We also test the accuracy of family knowledge by asking about their own existing insulation, their ranking of savings from various energy actions, and their methods for computing savings of recently installed insulation. We find a steady rate of retrofitting in Michigan, prompted by higher energy prices and by desire for greater comfort. However, we also find that insulation may not be installed, or may be installed in suboptimal quantities, due to families' overestimation of current insulation or underestimation of economic savings. We find that families measure their energy consumption in dollars. Therefore their calculated savings are underestimated because of failure to control for fuel price escalation. We conclude that more comprehensive, dwelling-specific, information services could greatly increase the efficiency of energy use in residences.