A mattress, foundation, or other upholstered sleep product or article includes a core and barrier material surrounding the core. The barrier material includes flame and heat-resistant material that is configured to prevent combustion of the core when the upholstered article is impinged with a gas flame according to California Technical Bulletin 603 of the State of California Department of Consumer Affairs. The barrier material may include an intumescent material that is configured to swell and char in the presence of a flame so as to form a barrier to the flame and to heat generated by the flame.