If you're converting a shipping container in Alberta - office, storage, workshop, tiny build - insulation is the make-or-break, and closed-cell spray foam is the near-universal answer. The reason is condensation: a bare sea-can sweats relentlessly, and only foam sprayed to the steel stops it.
Why closed-cell, not batt
- It bonds to the corrugations: foam follows the ribbed steel with no voids; batt leaves gaps that trap moisture and rust the walls.
- It stops the sweat: the vapour-controlling layer ends the condensation that defines an uninsulated container.
- Thin profile: a couple of inches gives real R without eating the container's narrow width.
Before you convert
Insulate before framing, wiring or cladding the interior - the sealed steel shell is the foundation of everything else. Plan for the thermal barrier if it'll be occupied.