Thermal grease

for 30 relays SG/SVT or 60 relays SC/SO/SA/SU

The surface of Solid State Relays or a heat sink is never entirely flat. If you mount a Solid State Relay directly on a heatsink, there will be invisible gaps between the two parts. Since air conducts heat poorly, these gaps have a very negative effect on the heat transfer. Therefore, an interface material with a high thermal conductivity is needed to fill these gaps to improve heat conductivity between SSR and heatsink.
You can decide between using thermal paste (or grease) and thermal pads.

Thermal Pads or Thermal Paste ? Differences and Advantages