Firediver
Contributor
If your trying to keep the drink warm, and your diving cold water.. it's not going to stay warm too long no matter how you insulate it.. because it isn't constantly giving off hear like our bodies.. unless you look at the dry suit warmers that are battery operated and can fabriacte a way of making it water proof in a neoprene sac with silicon bladder to hold your liquid of choice........ I know diving here in New Brunswick it gets pretty cold.. and I hot liquid won't stay hot long at all at in the water.