Janus particles are engineered to have two surfaces. One type of Janus particle has a hydrophilic side (attracted to water) and a hydrophobic side (water repellant). Until recently, Janus particles could not be produced in large quantities, and their commercial applications were unclear. Researchers mixed Janus nanoparticles with commercial paints and then painted surfaces to see how the particles would react. They found that the hydrophilic side oriented to the surface and helped the coatings adhere better, while the hydrophobic side faced toward the surface and made it water-repellant.