HI, all posts are good, but if you have lots of money, and want the very best insulation, it"s called Rubatex, 1'', which is pricey, and mostly used on chillers. I happened to get a roll from work and insluated my trailer with it, very easy to install, especally with the spray glue.
http://www.lcinsulations.com/rubatex...and%20roll.pdf
Rcpete