Living in a can

Life in a van is like living in a tin can. You are surrounded by metal with very little, if any insulation and it is cold and noisy. People who meet you think you don't have good taste and others just want you to get recycled.
I love the big "R". R value is basically the ratio of the temperature change from inside to outside, to the surface area. If the heat transmission from the warm side to the cold side increases then the temperature difference will be less per given area and the ratio will be smaller. If the heat transmission decreases then the temperature difference will be higher per given area and the ratio will be higher. R value is stated on the insulation material used and the R value the more thermal resistance you can expect.
In the van I use a closed cell foam (pink or blue) that has a stated R value of 3.5. I don't use the fiberglass batten type insulation because I don't want the fibers floating around in my nest. One loose fibre and I would be itchy for months.
I use expanding polyurethane foam to both glue the foam board to the metal side of the van and to fill the voids. The nice thing about using this canned glue/insulation is that it fills the gaps as it glues. The foam board can bed bent into place, but there are curves that the board foam can't match. The foam fills these gaps nicely, oozes out between the cracks and completes the insulation nicely.

 This is the one of the two back doors. There already was silver insulation glued to the metal in this door so I just glued the pink foam board on top. You can see the expanding foam oozing out.

 I use the little bits of foam as wedges to hold it all in place until it drys.

The long nozzle helps to get in behind the foam board to fill the voids. Once squirted, just stick wedge into place and feel the warmth. R 3.5 is not very much. With the silver insulation I might be getting R5.  Some surfaces in the van are layered with 2 pieces of foam and thus have an R value of 7! Today's energy efficient houses are built with R values ranging from 12 to 30.

When you live in a tin can, every little bit helps though. This makes a huge temperature difference inside my tin can and really helps to cut down on noise and condensation as well. One of the by products of propane and butane combustion is water vapor. Since I use open flames to heat and cook, the air borne water vapor is high. Keeping adequate air flow and insulating becomes critical. My wife, my son, our dog Gus and I lived on a 28' sailboat for over 3 years in the Canadian cold, year round from '02 to '05. Condensation was our constant nemesis then and it will be again now if I don't watch for it. It can lead to mould and mildew which is not healthy. But, if you have ever been woken out of a deep sleep by an ice cold drop of water hitting you square in the face, you know the better reason to keep condensation at bay.

Little adjustments in my tin can life style have made huge differences in my comfort level. Creature comforts take on a whole new meaning when you don't have many of them. Like the man who never worked with his back on a 12 hour shift who always has to have steak to please his pallet compared to the guy who labored in the mud and the blood wsho is very content with a couple of hot dogs at the end of a long day. When a hot dog taste as good as a steak, you have probably been doing something worthwhile.