How to avoid pipe insulation wreath kink!

So, there are lots of gorgeous wreath making tutorials out there and the top tip for making a wreath form on a budget is to use pipe insulation for the base of the ring. This is great because pipe insulation is cheap, this is not so great because pipe insulation is made for straight pipes, not ring-shaped ones. Wreaths made this way have a tendency to have bends or creases or kinks in them, as demonstrated below...

(Wreath wrapped in burlap and decorated with t-shirt roses made from this tutorial by Cathie Filian.)

After several craft nights where we have made projects for the kids I decided it was time we made something for ourselves and burlap-wrapped wreaths seemed to fit the Fall-time bill. Off I went to Lowes and bought lots of pipe insulation and came home and tried to form some rings. Not very easy to do when you want a nice round circle without any kinks. My main philosophy when I'm coming up with things for Craft Night is that they need to be easy enough for anyone to turn out something great, and I was having visions of people struggling with their foam trying to eke out something resembling a ring shape. Not good, so I decided to experiment...

I thought about stuffing, I thought about wire, (but I didn't really have anything suitable in the house and I'd left this to the last minute), so then I just thought about maths. The inside diameter of a ring is always going to be less than the outside diameter, so trying to form something that is parallel into a ring is not going to work unless one side is shorter than the other. One Aha! moment later and this is my solution for a nice circular pipe insulation wreath form:

The foam has a slit pre-cut in it to allow it to be wrapped around the pipe but usually this is not fully cut. Cut right through this along the full length.

Then tuck one cut edge into the slit.

Bend the foam into a ring. Tucking one side into the other allows them to move over each other and allow a shorter inside diameter, if you look at the ends you can see the extra length.

Cut this excess from the ends so they are parallel (this photo is before cutting). Tape ends together with duct tape.

You can see that this doesn't give a nice circular cross-section but once it is wrapped and decorated you can hardly see the difference, certainly less than you'd notice a non-round wreath.