Thermal conductivity is inversely proportional to thickness:

If the thickness of the thermal conductive silicone film is thicker, the surface temperature of the heated part will take longer to transfer from one end of the film to the other, so the heat transfer will be slower. At the same time, the thicker the thermal conductive silicone sheet, the more expensive (because the same size, the thickness of the thicker the use of more materials).

The relationship between thermal conductivity and hardness:

If the harder the product is, the worse the contact between the thermally conductive silicone gel and the heat generating parts and heat dissipating parts. The softer the more adequate contact (but not the softer the better, because too soft, not easy to paste). This can be explained by the following diagram.

When there is no thermally conductive interface material between the heat generating chip and the heat sink, the heat flow between the two connecting surfaces passes through the The path of heat flow between the two connecting surfaces is shown in the figure.

When a thermally conductive interface material is used between the heat generating chip and the heat sink, the path of heat flow between the two connecting surfaces is shown in the figure. The path of heat flow between the two connecting surfaces is shown in the figure.