3 Types of Rigid Foam Insulation:
Polyisocyanurate - best choice for walls and ceiling:
- Grey or yellow
- R Value of ~6.8 per inch (can vary among brands)
- After 5-10 years: R Value of 5.5 per inch (where it stays)
- Comes in 4' x 8' sheets
- Available at Lowe's and Home Depot
Use at least 4 inches. If it has foil backing, be sure to face that towards the outside (the warm side.) This product can be irritating to skin, wear long sleeves and gloves.
Extruded Polystyrene (XPS) - best choice for the floor:
- Pink or blue
- R Value of 7 - 8 per inch
- After 5-10 years: R Value of 5 - 6 per inch (where it stays)
- Comes in 4’ x 8’ sheets
Use at least 4 inches in the walls, floor and ceiling, and you'll be fine.
Expanded Polystyrene (EPS):
- White beaded
- R Value of 3.8 per inch
- Retains its R Value over time
- Comes in 4’ x 8' sheets
- Available at Lowes and Home Depot
EPS has the lowest R Value, so be sure to use at least 6 inches.