This is an expensive, brittle metal used to make the shadow mask in a direct view color picture tube. Incorporating it allows higher picture contrast levels from the tube without incurring long-term damage to the shadow mask itself. It allows the set manufacturer to offer you ever higher contrast levels. Since the phosphors in the tube reach the point of blooming well before the need for the Invar mask, anyone properly setting the contrast level for no blooming in the picture won't ever need the features of the Invar mask. The high contrast levels permitted by the Invar mask will eventually burn the phosphors. An Invar shadow mask has the potential of slightly degrading the picture quality when compared to a standard, well made shadow mask. The Invar brittle metal is difficult to drill, therefore the holes in the mask are not as well formed as they should be in a conventional shadow mask. This causes slight distortions in the picture. They of course would be hidden if the contrast were run high enough to need the assets of the Invar metal. If this Invar "feature" were to be removed from high end sets, real picture quality would go up slightly, and the cost to the manufacturer would go down. A large number of expensive sets, having many other desirable features, come with an Invar shadow mask. Its presence is not a reason to avoid the set, just an expensive option that you shouldn't need. If your set has to compete with sunlight, look for the Invar shadow mask. You'll need it.