How do you keep the milk warm at constant temp (say 40 degree c.) during outing? I tried with Pigeon double bottle holder but it does not work.

If the milk won't be consumed within 2 hours after it has been made, I suggest you make the milk only when your baby needs it. You can store your hot water in thermos flask such as Tiger Brand.

Pacific Baby has a thermal bottle range which you could consider using. It claims to keep milk warm for up to 10 hours. Essentially, it's a thermos flask but with a teat.

thanks