Originally, I also buy 保溫袋, but found it's not very useful since the hot water will be cool down after several hrs. So, now, I'm using a vacuum pot for hot water, then prepare some warm water in milk bottle for immediate use during transportation.
when you go out, you can put some hot water in a thermos flask and the put the cool boiled water in the milk bottle itself so you don't need to bring an extra bottle of cool boiled water.