Interior vs. Exterior Paint: What's the Difference?

Interior and exterior paint look similar in a can, but they're formulated for completely different conditions. Using the wrong one leads to a finish that fails — interior paint on an exterior wall peels and fades; exterior paint indoors can off-gas and resist cleaning.

Exterior paint is formulated to withstand UV, moisture, and temperature swings. It contains resins and additives that resist fading, mildew, and cracking. In Southern Utah, that UV resistance is especially important — the sun breaks down coatings that aren't built for it. Exterior paints also flex more to accommodate the expansion and contraction that temperature swings cause.

Interior paint is formulated for cleanability, low odor, and a smooth finish under indoor lighting. It doesn't need to resist UV, but it does need to handle scrubbing, resist stains, and hold up to daily contact. Interior paints are also lower in volatile organic compounds (VOCs) because they're used in occupied spaces.

The finishes differ too. Exterior paints often come in flatter finishes to hide surface imperfections, while interior paints offer a range from flat to semi-gloss, with higher sheens reserved for trim and high-traffic areas. Using an exterior sheen indoors can look harsh and be harder to clean; using an interior sheen outdoors can fail quickly.

There are also specialty formulations — elastomeric coatings for stucco, masonry paints, floor enamels, and cabinet-specific coatings. Each is built for a specific surface and condition. The right product for the job is part of what makes a finish last, and it's one of the things a professional painting estimate should address.