If you have a chamber machine, follow these instructions: Invest in a bag with a chamber (mesh-less design). The vacuum bag's open end has to be the same size as or smaller than your machine's seal bar, and the bag must also fit within the chamber. If you have an external-type machine (mesh design), you must purchase an external-type, or "out of chamber," bag if you have an external-type machine (mesh design). The vacuum bag's open end must be the same size as or smaller than your machine's seal bar. The content of every one of their vacuum machine bags specifies the size of the open end and whether you can use it with chamber or external machines.