They are plastic and are not air tight. These lids are so handy and are dishwasher safe. We love to use mason jars for storage and these lids make that easy and look neat too. Of course, you cannot can with them but they are great for storing open jars in the fridge.

Also, how do you sterilize glass jars with plastic lids? How to Sterilize Canning Lids and Jars

Wash all canning equipment in hot water with mild dish soap. Place lids and bands on a clean dish towel. Submerge jars in a boiling water bath for ten minutes. Leave jars inside hot water until ready to fill.

Similarly, can lids be reused for canning?

If youre planning on canning, you can reuse your purpose-made glass jars and screw bands, as long as theyre in good condition. The metal snap lids, on the other hand, are made to be used once. Once the gummy, rubbery seal on the lid is heated and cooled, it cant make the same quality of seal again.

Can jars be plastic?

A jar is a rigid, cylindrical or slightly conical container, typically made of glass, ceramic, or plastic, with a wide mouth or opening that can be closed with a lid, screw cap, lug cap, cork stopper, roll-on cap, crimp-on cap, press-on cap, plastic shrink, heat sealed lidding film, an inner seal, a Tamper-evident band