The best replacement for rigid foam is spray foam.

The best alternatives to rigid foam are rated as following:
★★★★★  spray foam
★★★★  fiberglass insulation
★  dricore

Your alternative for rigid foam is not listed? Suggest!
Speaking about rigid foam, one probably shouldn't forget about spray foam.

Other search terms related to rigid foam and their ratings are:
★★★★★ spray foam
★★ vapor barrier
You have in mind a companion for rigid foam and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of rigid foam in all years. Click on graph for more.
rigid foam
spray foam
fiberglass insulation