Droplets sit and slide anisotropically on soft, stretched substrates.

Anisotropically wetting substrates enable useful control of droplet behavior across a range of useful wetting applications. Usually, these involve chemically or physically patterning the substrate surface, or applying gradients in properties like temperature or electrical field. Here, we show that a flat, uniform, stretched, soft substrate also exhibits asymmetric wetting, both in terms of how droplets slide and in their static shape. Droplet dynamics are strongly affected by stretch: glycerol droplets on silicone substrates with a 23% stretch slide 70% faster in the direction parallel to the applied stretch than in the perpendicular direction. Contrary to classical wetting theory, static droplets in equilibrium take the shape of ellipsoids, oriented parallel to the stretch direction. Both effects arise from droplet-induced deformations of the substrate near the contact line.