thick metal below a pot

Why would you want to do this?

• They turn every pan into a cast iron pan, in terms of ability to remain hot after putting cold ingredients in them.
• They help eliminate hotspots.
• If you're doing multi-hour slow cooking, some stovetops — especially gas stovetops — aren't great at maintaining a steady low temperature. A diffuser will moderate the temperature, allowing all stovetops to do slow cooking and long-term simmering. It serves a similar role as a double-boiler, though it doesn't reduce the heat as much.

Some products you might consider:

• heat diffuser plates
  • copper heat diffuser [1] [2] [3]
    • TODO: Wouldn't the copper surface get lots of dents and dings, since it is a much softer material than the steel pans that will be moved around on it? Does it make sense to attach some steel sheet metal to the top? (whether by cladding or riveting)
  • aluminum heat diffuser
• I've seen people use a stovetop griddle (that typically straddle two burners) or a baking steel (possibly rectangular in shape so it can cover two burners), and using it as a surface that you can put multiple pots on.

There are two materials-science properties relevant here: