They aren't as light as others but my kids took the double insulated thermos which is what they use at school. I want to say they are 24 oz. I filled them up with ice, added bottled water, added more ice as it melted added water and even in the hot August sun they still had ice in their water bottle post mid day nap when I filled them up again.
Dh and I had the double insulated plastic ones we use for our bikes and while it kept the water cold for an hour or so after that it start led to get warmer.
So when we go again in 4 years I will get dh and I the thermos. Actually we are headed to FL in 3 weeks and I need to get them by then.