Hi Beth-Ro
I use a sigg water bottle which is aluminum and I have an adventure cycling neoprene jacket over it and it stays pretty cold. I also found ice cube trays that make long slim ice cubes to fit in water bottles. I pretty much put as many as I can in my bottle and then top off with water.
I think it was Veronica who has a Elite Keratherm bottle but I've never seen them in any LBSs around here, so maybe she can provide a link.