We demonstrate ultrathin (2 mm thick) red and orange polymer light-emitting diodes with unprecedented mechanical
properties in terms of their flexibility and ability to be stretched. The devices have a luminance greater than 100 cd m–2,
sufficient for a variety of optoelectronic applications including indoor displays. They can be operated as free-standing
ultrathin films, allowing for crumpling during device operation. Furthermore, they may be applied to almost any surface
whether rigid or elastomeric, and can withstand the associated mechanical deformation. They are shown to be extremely
flexible, with radii of curvature under 10 mm, and stretch-compatible to 100% tensile strain. Such ultrathin light-emitting
foils constitute an important step towards integration with malleable materials like textiles and artificial skin.