Acrylic skylights will often fog up after about five years, becoming cloudy and allowing less light in. Typical cleaners will not work on acrylic skylights. Also, they may become brittle and can even crack after about 15 years. Glass skylights are double-pane gas-filled glass that are far sturdier than the acrylic skylights. They can be cleaned and are less likely to crack than acrylic skylights.