The present invention provides a fiber-reinforced aerogel material which can be used as insulation in thermal battery applications. The fiber-reinforced aerogel material is highly durable, flexible, and has a thermal performance that exceeds the insulation materials currently used in thermal battery applications. The fiber-reinforced aerogel insulation material can be as thin as 1 mm less, and can have a thickness variation as low as 2% or less. Also provided is a method for improving the performance of a thermal battery by incorporating a reinforced aerogel material into the thermal battery. Further provided is a casting method for producing thin fiber-reinforced aerogel materials.