Recently took an on line quilting course where there was a lot of discussion about cotton vs. polyester. she used poly for FMQ but cotton for the piecing.

Got me to check the spools I have. I have been purchasing all purpose for years and saw on the spool they are polyester. I have do have few cotton and then some poly wrapped cotton. I don't keep my bobbins with the spool they came off of - just try to match the color.

So, it is possible I have been mixing the types of thread when sewing, which could account for some tension problems?

Oh, I need to be more carefuly and I'm going to sort my threat not only be color now but also by type!

I guess I have been doing it wrong also.

I don't know if there is truly a "right" way as far as which thread to use - I guess that's debatable.

I do think that you may be right about tension though. As long as you're aware of the difference in the threads, you can mess with the machine's tension to get it right. I sometimes use poly in the bobbin and cotton on top - works alright.

All poly scares me. I once did a bunch of paperpieced blocks with poly thread. I pressed them too much and every single one had seams popping open. It was devastating. Tough lesson learned on a number of levels....

I've always been wary of using poly thread since the days of owning a laundromat and seeing people drying their comforters on high heat. They would wonder why their quilts/comforters would start to unravel and I would point out that the polyester thread was melting in the dryer. Mostly it was mass-produced items (made in China, etc,) but I've never seen any articles on the heat resistance of poly thread bought here. Any thoughts?

I never thought of polyester thread melting. Not until the other day when I embroidered a pocket purse in the hoop. When I took it out I needed to fold it into 3. Well, why not make a neat job and iron it. My iron is set on cotton setting and I never thought a thing about the heat. I ironed it flat and the thread melted. I was quite shocked when I looked at it and it was soo shiny all over the fabric. Then it hit me....I learned a very valuable lesson that day. However, I never thought of the dryer causing this problem. Thanks for mentioning that.

I recently ordered the free DVD from Superior threads. Bob, was the lecturer and it was a truly informative and interesting thing to watch. I learned how come some threads work well and others don't. Why some work better in the bobbin than on top.

I don't know if it's still available but it it is you should try to get it. They don't promote one thread over another, but give you tips on figuring out which is best for the job.

Yes it is available until Jan. 31 and the cost is free....you only have to pay the shipping...the regular price is 24.95.

Bob of Superior Threads has a great Education page ... lots on threads (free) https://www.superiorthreads.com/education/