Energy-efficient windows are judged on their performance according to a few different factors, including heat transfer, air leakage, light transference, and condensation resistance. If you're unsure whether a window is energy-efficient, look for an ENERGY STAR® label from the U.S. Environmental Protection Agency (EPA). If various products, including windows, meet energy-efficiency standards set by the federal government, the EPA issues this label to help consumers identify energy-efficient products.

To darken your windows without curtains, try installing window film or even installing an awning outside your windows. Window film is a DIY-friendly option with many different darkness levels you can choose from to fit your desired look. Awnings can also help by casting shade over your window, though this isn’t feasible for every home. 

The ideal thickness of window film depends on various factors and specific needs. Thicker films generally offer increased durability and enhanced security benefits. They are also typically more effective at reducing heat and blocking UV rays. However, thinner options may be preferable for some applications, such as decorative or privacy films. Thinner films are easier to apply and provide adequate privacy without compromising visibility. Ultimately, the best thickness of window film will depend on your specific requirements, desired benefits, and the recommendations of professional installers.

ENERGY STAR®-certified windows are the most energy-efficient windows on the market. This certification means that the window meets strict efficiency guidelines set forth by the Environmental Protection Agency. While they might cost more upfront, they can save you money on your energy bills in the long run. ENERGY STAR®-certified windows lower household energy bills by an average of 12% annually.