What requirement must cabin upholstery materials meet in standard category airplanes?

The requirement that cabin upholstery materials must meet in standard category airplanes is that they be at least flame resistant. This is crucial because the primary concern in aviation safety is to minimize fire hazards. Materials used in the cabin are subjected to strict flammability standards to help ensure that in the event of a fire, the materials do not contribute to its spread or intensity.

Flame resistance is classified according to specific conditions and testing protocols that simulate potential onboard scenarios. Materials that meet these standards are treated or designed to resist ignition and slow the spread of flames, thereby giving passengers and crew additional time to respond in emergencies. This requirement is in place to enhance overall safety in aviation and protect passengers from hazards while in flight.

While other qualities like being lightweight or having high tensile strength can be beneficial for performance and durability, they do not address the critical aspect of fire safety that regulation seeks to enforce in standard category airplanes. Waterproofing may be useful in certain contexts, but it is not a primary requirement for cabin materials like flame resistance is.