range hood ducting with thermal break

I am planning to install a range hood. A couple of sources recommend adding a nonmetallic thermal break between the duct that runs out to the exterior wall cap and the duct that runs back to the range hood--placing it as near to the wall as practical. This seems like a good idea for someplace like Minnesota.

Except for the suggestion in one of the above references to use a "short length of nonmetallic duct", I have not seen anything that actually suggests specifically how to implement this thermal break. I have not seen 6" diameter nonmetallic duct anywhere--unless 6-inch PVC could be used.

I was hoping to learn how someone else actually did this.

thanks