You might not know the director of Basket Case and Frankenhooker became an accomplished documentarian later in his career. Not that he changed focus from the grubby grindhouse to high art, but That's Sexploitation is as entertaining as it is fully researched.

With most of the background coming from an aged producer who was the same thing for sleazy sex movies as Roger Corman was to low budget schlock horror, Henenlotter looks at the history of sex on screen and the sometimes-incredible feats filmmakers would go to get around censorship laws and put it there.

You might not know there was a burgeoning genre of movies about nudist camps in the 60s and 70s, for example, which were marketed almost as documentaries, or that there was a movement of educational sex films showing explicit sex and doctors on hand to explain the vagaries of human sexuality. In one hilarious clip the same set – even down to the ashtray on the desk – is used by two different actors (pretending to be doctors) in two seemingly unrelated sex movies.

From the 3D bikini thrills of the 50s until the VCR era, it's a historical document that remembers a time polite society would rather forget. It's almost made even more poignant by the fact that – like so many other media that rode (excuse the pun) the selling of sex – it was finally undone by the video and Internet era, which effectively ended censorship altogether.

Helenlotter has a style that's somewhere between down home folksy and schoolboy snigger, and you can watch the film for the dozens of scenes of antique nudity (the hairstyles! The pubic hairstyles!) if you like. But if you've ever watched a short clip on a porn site, it's worth learning how scratchy sepia-toned clips you put a dime in a machine to watch at a fairground led almost directly to it.