We are about a couple of weeks to pour concrete for the home we are building in Tucson, AZ. My builder told me that he will be using a Radiant Barrier under the concrete slab and he has found it to be very effective for this desert weather. I asked him if it is better to add Ployiso foam along with the Radiant Barrier. He said, that might not be necessary and I might be spending money unnecessarily as he will be using something like this: https://www.ecofoil.com/collections/under-slab-insulation which he thinks is already quite effective. He asked me to do my research and let him know if I want the Ployiso foam too to be added. What do you suggest?

That is 50 cents per sqft of nothing....show me a real certified study of that stuff working....Extruded Polystyrene (EPS) is the logical one to use (check termite potential issues). Not sure in Tucson, AZ why you would even insulate the floor to me you average high is 86 and average low is 50 so your average all year is 68 which is perfect temp and am guessing 68 is your normal ground temp 4 feet down. No insulation will only help your house stay the perfect temp all year around.

Your welcome.....

Thanks for your reply. I think you are right that Tucson doesn't require insulation under the slab. No other builder I had talked to told me they would do such insulation. The reason why we want insulation is, we will be getting stone flooring. The stone can get cold during winter (though it's mild here) and we would want to do what we can to keep the floor walkable bare feet. I thought the radiation barrier might be useful for this weather. There is no point in spending too much money for little gain given the climate of Tucson.

What do you suggest?

Also, Radiant barriers require an air gap for the reflective properties to work which can't be done in concrete. Have a great build....it is fun....everyone should do it once in their lives...