Soil Machine PROThe Soil Machine PRO is another good idea from Good Ideas. 7 cubic feet of composting capacity and over 5 gallons of space in the base for harvesting compost tea. The Soil Machine PRO is made of 100% recycled black Polyethylene resin. The dark color helps heat the inner chamber by absorbing light and heat energy. And you can feel good that it's recycled. The PE construction makes the bin and base strong and rugged. The unique shape of the Soil Machine