Just came across this video <https://www.youtube.com/watch?v=VJC6OpGpq0Y>, latest in a series on cooling solutions for a Raspberry π 4. This instalment looks at a couple of purely passive, fanless products that use the case as a heat sink (or vice versa). But on top of that, a recent firmware update from Broadcom has made a massive difference to the running temperature in all the configurations. Summary: passive cooling worked quite well before the update, and now works even better.