Dear K.Sonyakrich :
Here is temperature data around solid state relay, during oven running measured by Infrared thermometer.
From this data, action to insert plastic plate under heat sink is not enough.
Temperature is same level for original oven and No.29 oven.
We may need 2 kinds at a time.
One is to insulate heat sink from oven body to prevent heat transfer from oven body to heat sink.
The other is to increase heat radiation from heat sink. --> need more air flow…