They do not have to freeze to return, took mine from house to car , outside temp 42, lines had returned by the time I arrived, 2 hr trip in warm car.

Thanks for the tip

There have been lots of discussions here about those pens. I hesitate to use them. When I first discovered them a couple of years ago, I did a lot of research and nowhere did I find that they were acid-free. Someone recently told me that Pilot NOW says they are acid free. I know the ink disappears when ironed, but the simple fact that the ink reappears when cold makes me wonder what else stays in the fabric.

Also, there have been some quilters who have said the lighter pens on darker fabric leave yellowish lines. I think I'm going to stick with pens that are manufactured specifically for marking quilts - that's the only way I'll feel safe.

I have not tried these, but will be soon!

I have used them and found that they are fine on some colors, but on dark colors I have had faint white lines as though they bleached the color right out. On one baby quilt I had drawn a cross hatch pattern in blue on a red color. After I ironed it, there was a very faint white cross hatch pattern on it.

My bedroom has no heat, so I would never use them.

I picked some up at Walgreens!

These are the greatest pens in the world.

I really like them. The marks have all disappeared with ironing and I don't freeze my quilts, soI don't worry about the lines returning. Also, if you wash the quilt, the lines don't return. Better than anything else I've found for marking.:)

Thanks for sharing - I purchased one & haven't tried it yet so it's good to know it works!