There is a little learning curve in using them. Don't tighten down the rings as tight as you usually do. There has to be some room for air to escape. I tend to leave about 1/4" more head space to prevent boil-overs especially if it has to be done in a pressure canner. I have had about 95% success rate with them sealing properly and have found the failures to be caused by filling the jars a little too high or tightening the rings too tight before processing. Generally, if you put the rings on then turn back about a quarter of a turn to loosen again you will be fine. The packages come with instructions that are very helpful. I bought mine from lehmans.com Happy canning!!