Upgrade to double-glazed glass or apply energy-efficient coatings to reduce heat loss and utility costs.

Some frosted glass sprays can handle the outdoors, but most of them aren't built for it. Sprays made for exterior use will say so clearly on the label. Anything marked “interior use only” can't hold up against rain, UV exposure, or changing temperatures without peeling, fading, or yellowing. Outdoor-rated sprays are typically more durable, but even then, proper prep and application matter. Before spraying anything outside, double-check the product instructions. If it doesn’t specifically mention exterior use, skip it. 

No, it isn’t necessary to have energy-efficient windows. However, if you care about your energy bill and making your windows more energy efficient, fixing any heat, UV, or air transfer issues is an excellent way to lower your bills and keep your house cooler in the summer and warmer in the winter.

Whether window film is better depends on individual preferences and specific needs. In some instances, window film can be much less costly to install. Aesthetics is also a deciding factor. Window film may have a more significant appeal for design minimalists looking for a clean and streamlined look without the heaviness that comes with curtains. On the flip side, they can also appeal to design maximalists looking for creative expression in the form of color, patterns, and texture. Choosing between window film and traditional window coverings depends on factors like desired functionality, aesthetics, and personal preferences.