Homebrew Carboys are glass containers that homebrewers use for fermenting beer. Carboys come in a range of sizes, from one gallon to six gallons. Glass carboys do not allow oxygen to pass through. With careful care, carboys will be reusable for many brews.
Be very careful not to set your filled carboy on a surface that is not clean and smooth, like concrete. You don't want to create pressure points that could crack the glass. Always set your carboy on a piece of wood, cardboard, towel, or rug.