Why the cloth?

The cloth squares on the jam jars are reminiscent of good homemade products from both Quebec and France. On older containers, which existed even before screw-on lids existed, there is a groove to secure the cloth covering to the jar. The fabric was presumably used to protect the contents!

© Pointe-à-Callière, cité d’archéologie et d’histoire de Montréal
Jar from the 19th century, with groove to maintain the piece of clot.

Source : https://www.archeolab.quebec/recherche/objet/236175