Question about Bandcamp - CD production?

[MitchT]

I'm not on Bandcamp at the moment - need to get some music 'finished' enough to be able to sell it first, however, I am exploring the options. I love the idea of the vinyl style CDs but what I can't find out from the website is what basis they're produced on. Do you have to pay for a batch making and then hope you can sell them, or are they produced by Bandcamp on an 'on demand' basis, so you have no upfront cost and they simply deduct their manufacturing cost from the selling price?