I used some left over scraps from a dress I made a few years ago when I was learning how to do the FBA. The dark turquoise is from a pair of girls' pants that came from a friend of my MIL. It's not actually as dark as in the picture; it's quite bright. I used the pant hem around the top and didn't want to stitch through it when joining the print, so that's why there's a border. I had to do a seam in the strap, but oh well. I keep having this issue where I cut the strap the full width, instead of cutting two straps, each 1/2 the width.
In the end, I couldn't get my aluminum backed foam in between the layers. I didn't think about needing more ease to allow for that. Then, I used the foam to wrap hot dogs in Lucy's camp lunch and she says they weren't warm at lunch time. So, I don't hold much hope for it. And anyway, the aluminum is on one side only; once reversed, then the foil is on the other side (hidden between the layers). One way it would be reflecting the outside heat, the other way it would be reflecting the bottle's temperature. Would that matter? I also like how these holders are squishable for packing. With the foam in them they wouldn't be quite so squishy.
I really like this holder, though I do think the wool ones keep the water colder!