At a 100-yen shop (100-yen shop), I found "Kurukuru COOL", an ice pack for PET bottles. I actually bought it and used it. The price is 108 yen (tax included).
This is a convenient ice pack that can be wrapped around a PET bottle to keep the drink cold. Compatible with 350 ml and 500 ml. Illustrations of cute polar bears, penguins, and seals are printed on the ice pack.
After cooling in the freezer for 6 hours or more, wrap it around a PET bottle and cover it with a PET bottle case. It's a type of ice pack that doesn't harden even when frozen, so it's easy to wrap it around a bottle! However, please note that the ice pack itself is thick and may not fit in some PET bottle cases. If you want to combine them, we recommend a PET bottle case with plenty of size.
"Kurukuru COOL" is a 100% PET bottle ice pack that seems to be useful for keeping "cool". It seems convenient to have one type to wrap. Why don't you pick it up when you see it?