A proof-of-concept subscale prototype of a lightweight, low-cost inflatable heliostat features a spherical inflatable structure with a reflective Mylar membrane mirror on its equatorial plane. The reflective surface is protected from rain, dust, sand, and wind by the transparent upper hemisphere, and can be shaped to achieve varying focal distances through differential air pressure between the upper and lower hemispheres. While the prototype transparent surface is made of heat-seamed optical vinyl panels, a potential production application would use single-sheet thermoformed Tefzel, which features high transparency, long field life, and a self-cleaning characteristic. The inflated sphere is stably supported by a combination of polar bearings and base rollers, and the entire sphere can be precisely pointed in elevation and azimuth angle using two stepper control motors. Preliminary estimates indicate that inflatable heliostats could potentially reduce heliostat cost from around $192/m2 for conventional glass mirror heliostats down to around$67/m2...