An epoxy resin system composition and a loss circulation material including the reaction product of the epoxy resin system are provided. The epoxy resin system includes a polyhedral oligomeric silsesquioxane (POSS) epoxy resin with at least one reactive group, a curing agent, and a CO2 gas-generating compound. The CO2 gas-generating compound generates CO2 during the reaction such that a volume of the lost circulation material is greater than a volume of the epoxy resin system. A method of treating a defect in a wellbore includes introducing the epoxy resin system into the wellbore such that epoxy resin system is proximate to a face of the defect, and maintaining the epoxy resin system at the face of the defect such that the epoxy resin system cures and a lost circulation material forms and fluidly seals the defect in the wellbore.