vellum is typically stored in a stable environment with a stable temperature. if vellum is stored in an environment with less than 11% relative humidity, it becomes fragile, brittle, and susceptible to mechanical stresses; if it is stored in an environment with greater than 40% relative humidity, it becomes vulnerable to mold or fungus growth. the best temperature for the preservation of vellum is 20 ± 1.5 °c (68 ± 3 °f)