A vacuum seal is not necessary, but the package must be air tight. You cannot expect perfect results if you use ordinary foil, wax paper, thin plastic wrap, or similar materials. Plastic freezer bags may be protected with a cardboard box to keep from tearing. Rectangular cartons stack easier and make better use of freezer space than irregularly shaped packages. Rectangular cartons stack easier and use less freezer space.
Rigid containers hold their shape, stand upright and stack well.
Be sure they have tight-fitting lids. They may be plastic containers, which are available in square and round shapes. Heavily waxed cardboard containers, with plastic or waxed lids, are also good to use. Canning-freezing jars are best because they are tempered to withstand both extreme cold and heat. Handle glass carefully because rough handling or sudden changes in temperature can break the glass.