Foil insulation was commonly used underfloor in the past and it does provide insulation from radiant heat loss but does not have an R-Value like bulk insulation. Existing foil insulation is only effective for radiant heat loss if it is intact (not ripped) and is neither dusty or tarnished.
If you do not already have underfloor insulation installed, foil insulation is not accepted as a solution under the Residential Tenancies Act.
