The bottles aren't actually made from some indestructible self-repairing glass material discovered in a secret lab a decade ago; they're plastic, which is why they can be squeezed without shattering. However, the insides of the bottles are coated with an incredibly thin layer of silicon dioxide—which is what glass is made from—that's just 20 nanometers thick. It acts as barrier preventing smells, flavors, mold, and other bad stuff from sticking to the plastic, but it remains completely flexible.
The Squeezable Glass bottles' inner layer will never rub off, but even if it were to, silicon dioxide is FDA-approved for direct food contact, and it naturally occurs in fruits and vegetables. That added layer of protection also means these bottles can be just tossed in the dishwasher for cleaning, and they start at just $15 with a seventeen-year warranty, which will have you wondering why anyone would ever consider a Nalgene or Camelbak ever again. More here.