Insulation and conduction are opposites. Vacuum (empty space) and stagnant air are great insulators, that’s how double walled bottles insulate.

Aluminum conducts heat quickly for the same reason it conducts electricity well. It has a relatively low heat capacity too so it doesn’t take much energy to heat or cool it so it will more quickly heat or cool its contents.

Toss that alu can in the freezer to cool it quickly, then put it in an insulated colster to keep it cold.