"VivienB"
Easier still, re-use screw-top jam jars. Put the lid on as tight as
you can as soon as they are filled - they form a vacuum as they
cool,
pulling the rubbery seal tight onto the top edge of the jar. Voila -
home-made jam *and* recycling (OK, re-using) all in one go.

Works even better if you turn the filled jars upside down to let them
cool off ~
Jenny