From zori straps to a molded foam sole
The key design idea is simple: a flat sole stays under the foot while a strap passes between the first two toes and branches over the sides. Japanese zori sandals used this arrangement long before today’s beachwear. Their soles and straps could be made from different materials; the recognizable shape did not depend on rubber or foam.
That arrangement is practical because it holds a sandal in place without covering the top of the foot. It also makes the footwear easy to slip on and off. The thong between the toes provides the anchor, while the two side straps help keep the sole from sliding away with each step.
Why the modern version is so easy to make
Modern manufacturers can reproduce the basic form with molded foam or rubber. The sole is shaped as one lightweight piece, and the straps are fitted through openings in it. This avoids the more involved weaving or layering used in some traditional sandals, helping make the modern version inexpensive to produce and simple to clean.
The result is a familiar design carried across a change in materials and manufacturing: the lasting feature is the strap-and-sole arrangement, not the substance it is made from.
