My mind was wandering today. I was looking at bathtubs b/c I'm too tall for mine and one of the problems of tubs is heat waste and conductivity. This explains why I can take a bath for only about 5 minutes before the water gets tepid, then chilly. After a brief ride on the information supa' highway I found that some people say a layer of bubbles will actually insulate the water from the air. Interesting but I think the tub is the bigger problem. A few internet solutions were to foam insulate everything, the pipes, the water heater, and the tub, as well as preheating the tub and refilling. Others say to keep a small trickle of hot water going to prevent large dips in temperature. Seems pretty inefficient to me.
Most bathtubs are made of metal (iron, steel), some are ceramic (acrylic), some are stone (marble), and others (fiberglass, polymers, resins). Metal has high conductivity, ceramic and stone stay cold and the others have varying properties.
Maybe the tub needs to be taken out of the equation, and the basin could be built out of solid forms. Maybe a water re-heater is necessary.
What does everybody think? How can we design Maximal water heat retention tub? Materials? Techniques? Anyone have thermal ratings for tubs and materials?