No, the Impossible Project film isn’t “instant.” I have taken to referring to it as “self-developing.” 
However, Fujifilm didn’t go out of business so they’ve got a few years on Polaroid. When Polaroid ceased production of their instant film, their entire supply chain was dismantled. Nothing was left. The folks at Impossible came along and “rescued” the factory in the Netherlands and began to resurrect the process of making the film. Everything: the chemical soup, the negative materials, the white mask, had to be recreated and new sources found.
Sure, the Impossible film (now Polaroid Originals), is a far cry from “instant” but it’s massively improved in just the last few years and is getting better all the time.
Do I sound like an apologist? Sure. I like “instant photography” and own a handful of Polaroid and Instax cameras.
How could “real authenticity” (someone trademark that) have been had for cheaper?
