We use canning jars for a variety of purposes.  Two of those purposes include agar (i.e. Petri replacements) and grain inoculation. When using jars, we usually need to use lids with a small amount of air exchange.

We have tried both the metal lids and the plastic lids with jars.

Notes:

1. We prefer using the plastic lids over the metal lids
2. The medical tape (2 pieces, one perpendicular to the other) works well with the plastic lids
3. The plastic lids are very easy to twist on/twist off, making work in front of the flow hood faster
4. As the plastic lids are easy to take off, they can become loose in the pressure cooker. This is a risk
5. The medical tape needs to be smoothed down before using the lids – it also comes off fairly easily
6. The holes are easier to drill in the plastic lids than the metal lids
7. The metal lids stay on in the pressure cooker, there is no risk of them twisting loose
8. The metal lids rust over time. They must be inspected before using them
9. When using the metal lids, we prefer using the poly-fill in the hole(s). Make sure it’s tight in the hole, otherwise you will get unfiltered air exchange.
10. Plastic lids are more expensive to buy than the metal ones

Tips:

If you are using the metal lids, drill holes with a drill press. Keep the metal discs in their cardboard box and drill a hole (or holes) through the entire box. That way you only lose one metal disc to rough edges.

There is a warning on the box that the plastic lids are not to be used for canning. That is true! However, since we drill a hole in the lid the pressure does not build up in the jar. We have successfully used the plastic lids many times in the pressure cooker.