This is a piece of foam that was used on the Discovery. The shuttle fuel tank is the single largest part of the space shuttle. It is also the only part of the space shuttle that cannot be refurbished and reused on multiple missions (in other words, the fuel tank is ‘disposable’). The one inch layer of polyurethane foam slightly increases the structural integrity of the fuel tank while providing optimum insulation. Foam is ultra lightweight as well, which keeps the weight of the fuel tank at a minimum. Closed cell foam contains millions of tiny bubbles which trap vapor and seal a surface. This prevents air infiltration and creates a tight seal. Special compounds are used to clean the fuel tank surface before applying the foam. No adhesive is required; the foam self-adheres to the surface of the tank with enough strength to withstand the rocket launch (and even the fall back into the atmosphere; for the most part).

Polyurethane foam is pale yellow when first applied (this is the color of the fuel tank for the indoor pictures). After being outside for a period of time, the color of the tank shifts to orange. As ultraviolet rays from the sun hit the outermost layer of the foam, the material begins to break down on the surface. This does cause a small loss in insulation quality. Early on, NASA coated the the foam white to protect it from UV degradation. However, the paint added 600lbs with little benefit. Subsequent shuttles used bare, uncoated brown foam as a weight saving benefit.