Hybrid sol - gel materials have been a subject of intensive research during the past decades because these nanocomposites combine the versatility of organic polymers with the superior physical properties of glass. Here, we report the synthesis, by spin coating, of hybrid interpenetrating networks in the form of free-standing nanomembrane (around 35-nm thick) with unprecedented macroscopic size and characteristics. The quasi-2D interpenetration of the organic and inorganic networks brings to these materials a unique combination of properties that are not usually compatible within the same film: macroscopic robustness and homogeneity, nanoscale thickness, mechanical strength, high flexibility and optical transparency. Interestingly, such free-standing nano films of macroscopic size can seal large openings, are strong enough to hold amounts of liquid 70,000 times heavier than their own weight, and are flexible enough to reversibly pass through holes 30,000 times smaller than their own size.