Is it normal to see zero temperature change with AtticFoil?

The fact that you have solar panels on the west side is a huge factor here. Solar panels essentially act as a giant radiant barrier themselves; they absorb and reflect a massive amount of solar radiation before it ever hits your shingles. By stapling foil under that specific section of the roof, you're basically adding a second shield where one allready existed, so the marginal gain on that side is going to be almost invisible in your data.

Another thing to consider is that radiant barriers are designed to stop **radiant heat transfer**, not necessarily to lower the ambient air temprature inside the attic. Your Govee sensors are measuring the air. If your attic lacks a ridge vent and relies only on those four louvered vents, you have a massive ventilation bottleneck. The heat that does get trough—or the heat that builds up from the roof deck—has nowhere to go. It just sits there. Without a strong thermal siphon to pull cool air in from the soffits and push hot air out the top, your attic air remains a stagnant heat soak regardless of the foil.

You also mentioned having a thick layer of cellulose and fiberglass on the floor. That is already doing the heavy lifting of keeping the rooms below cool. A radiant barrier's main job is to keep the top surface of that insulation from getting scorched by infrared radiation. If you want to see if the foil is actually doing anything, stop looking at the air temperature and get an **infrared thermometer**. Aim it at the top of your insulation. You will likely find the surface of the cellulose is significantly cooler than it was before, even if the air around it is still a furnace.

It is not a scam, but it is often marketed as a silver bullet when it is relly just one piece of a system. Without fixing the ventilation to exhaust that trapped air, the foil is just bouncing heat around a sealed box. You need that hot air to actually leave the building for your sensors to show a real drop. And since you already have thick insulation on the floor, the change in the rooms below will be subtle rather than a total transformation.

I've crawled thru more glass-filled attics than I care to remember, and I’ve seen folks get suckered by the 'silver bullet' marketing before. Back in my day, we focused on air sealing before we even looked at radiant barriers. If you haven't moved that cellulose aside to foam-seal your top plates and wire penetrations, that foil is just a shiny band-aid. Heat doesn't just radiate; it hitches a ride on air currents. If your ceiling isn't airtight, that attic heat is just 'drifting' down through the gaps in your framing. Grab a can of Great Stuff and get to work on the bypasses first.

Spot on about the surface temps. The foil is doing its job, but you’re likely still feeling the heat trough thermal bridging. Even with the foil stapled up, those wooden rafters are still soaking up heat where they touch the roof deck and conducting it right past your barrier.

Since you don't have a ridge vent, those rafters stay hot for hours after the sun goes down, acting like little radiators. The foil stops the infrared, but it can't stop the physical conduction through the wood itself. That’s prolly why your sensors aren't budging yet.

I just got a huge roll of this stuff delivered today and I am SO pumped to get started! Even if it's just a tiny bit cooler, I'll take it. But hey, while I'm up there crawling around, has anyone ever tried using the leftover foil scraps to wrap their water heater? My neighbor said it helps keep the water hot longer but he’s kind of a nut. Also, does the foil mess with cell service? I'm super worried I won't be able to stream my podcasts while I'm working in the attic!

Update: You guys were right about air sealing. I pulled back the insulation and found huge gaps in the top plates. After foaming those, the Govee sensors finally showed a real temprature drop. Turns out the foil was working, but those air leaks were sabotaging the whole thing. everthing is feeling much cooler now. Thanks for the solid advice!