What is the purpose of "backing material" in fabric covering?

The purpose of backing material in aircraft fabric covering is primarily to provide additional support and help distribute loads evenly across the surface of the fabric. When aircraft are in flight, the fabric is subjected to various forces, including aerodynamic pressures. The backing material reinforces the outer fabric, preventing it from tearing or stretching unevenly which could compromise the integrity of the covering.

In terms of support, the backing material can help to maintain the shape and structure of the aircraft, which is critical for its aerodynamic performance. It allows for a more even distribution of stress and load, minimizing the risk of localized failures that could arise from overstressed sections.

The other options relate to specific protective qualities but do not encompass the primary structural function of backing material. While backing materials may contribute to color appearance, moisture protection, and UV resistance indirectly, their main role lies in enhancing the strength and durability of the fabric covering system.