The print bed is custom because the peachy uses a laser to print. See the video on the home page of http://www.peachyprinter.com . At 00:12-00:15 into the video, you can see the complete printer, a 4 inch plastic contraption with a circuit board and the lasers and mirrors and whatnot. This little printer can be mounted to whatever you choose. It shoots the laser into a pool of resin that floats on top of saline. These are the reservoirs we are discussing, the upper reservoir being full of saline, connected to the bottom reservoir, which contains the print bed. The print bed is any surface you choose that resin will stick to, but is currently 1/4 inch steel mesh, raised away from the lower res with risers of some kind, bolts or bits of hose, whatever will work. At :30-:36 you can see the same printer set up with three different reservoir sizes. If you look carefully, you can also see the saline solution with resin on top. The saline drips into the lower res and the drips are counted by the printer, this, along with some calibration, is how the printer knows what the z axis height is. Feel free to ask more questions if this doesn't explain.