We construct a new dataset tracking the daily value of life insurers' assets at the security level. Outside of the 2008-09 crisis, a $1 drop in the market value of assets reduces an insurer's market equity by \$0.10. During the financial crisis, this pass-through rises to 1. We explain this pattern by viewing insurance companies as asset insulators, institutions with stable, long-term liabilities that can ride out transitory dislocations in market prices. Illustrating the macroeconomic importance of insulation, insurers' market equity declined by $50 billion less than the duration-adjusted value of their securities during the crisis.