Background Reading: 4-U: About Insulation

Tips:

-Unless you’re in an extremely cold climate, don’t worry out about what kind of insulation it has – as long as it’s decently insulated, the difference in your heating bill will be negligible if you’re in a mild climate.
-If the hot tub will be in extremely cold temperatures, make sure you have a good, thick cover, preferably one that includes an insulated runner strip under the seam gap 
-If you want more insulation in a model you like, instead of choosing another brand or ordering the full-foam upgrade, an easy fix is to stuff Rockwool or pink insulation between the cabinet and the shell.  It’s cheap & easy, and the fact it can be conveniently removed makes it much easier and cleaner to find and repair leaks in the future.