Butterfly wings were the inspiration for creating 3-D photonic crystals: They both appear brightly colored because they diffract light and also strongly repel water. In Shu Yang's research group at the University of Pennsylvania (U.S.A.), the researchers developed a simple method for creating the structures using lithography, and then for making it hydrophobic, by using a poor solvent that roughens the surface enough to repel water but not enough to change the photonic bandgap in the IR (Adv. Funct. Mater. 22, 2980). This surface treatment could allow solar cells to remain cleaner—and thus more efficient.