heatsink (ceramic)

Such airflow can be created via convection heating up the air within and around a heatsink so that the air flows up and away which then draws in cooler air towards the heatsink. The result is a natural convective airflow without needing fans to move the air over the heatsink. Obviously, increasing airflow speed over a heatsink will increase the amount of heat that can be moved into the airstream which is why we use fans when needing to remove larger amounts of heat from a given volume.

Conductive heat transfer is the ability of a material to move heat within itself. This is how heat gets from a chip to the heatsink (via the thermal paste acting as a bridge between the two materials). Aluminium is a worse conductive element than copper but silver is the best conductive element know to man. Ceramic space shuttle tiles would not be a good choice for a heatsink within our computers

The heatsink, be it ceramic or silver, is still limited by the rate at which it can reject heat from itself into the air via the convective process. This rate, in part, depends on the surface area of the heatsink, the rate of airflow, the ambient temperature (and the conductive coefficient of the heatsink itself). Increased heatsink area and increased air speed are the simplest ways to inceases the amount of heat one can reject into the airstream. This is why heatsinks are shapped like porcupines as the surface area with spikes is much much larger than a simple flat structure. But the biggest bang for buck is air speed which is why fans are so widely used (and silver is not).

So, if you want greatest heatflow out of some chip, get a silver heatsink and the best thermal paste on offer (guess it would be silver metal based material) and push as much air over the heatsink that you can managed. At the end of the day, the air speed will make the biggest difference.

However, since the RPi puts out a pittance of heat, it doesn't need any cooling beyong what can be handled via natural convection from the SOC area itself.

In reality, a flat heatsink aound the size of the SOC made from silver (best conductive element known) or ceramic (unknown conductive coeficient) would be just like having no heatsink at all, since the convective heat transfere is related to SOC area and air speed over this area. So IMHO, you'd be buying a flat ceramic heatsink and thermal paste for no reason.

By far, the biggest issue for RPi in a small case is that we can restrict the convective airflow which will redeuce the natural heat extraction from the SOC. In part, this is why many cases have slots around the GPIO pins and sides to let in cooler air while gaps around the top let the hot air out. Sometimes the conductive airflow can be minimised when connecting 40pin cable to GPOI as less cool air can get in which could result in higher SOC temps. Many have found that simply taking the top off in such situations is enough

Alternatively, either the case linked to earlier or the Kodi case, are both heatsinks in and of themselves. These case suck the heat from the SOC through the termal paste/pad using conduction but then radiate the heat from the case top into the air using natural convection. As the case top is more than 10 times the area of the SOC, it will be much much better at rejecting heat into the air as compared to some marginally larger (than the SOC) flat ceramic heatsink (which is inside a case and has the issues of airflow). Natural airflow over the case top case is more than in excess of what's needed to keep things cool with the only downside being using GPIO hats may not be able to be used within the case. Still, it's not needed from a cooling perspective but i like the Kodi case..

As Klojum said, no need for need extra cooling solution even if moderately overclocked RPi

A heatsink needs airflow.Such airflow can be created via convection heating up the air within and around a heatsink so that the air flows up and away which then draws in cooler air towards the heatsink. The result is a natural convective airflow without needing fans to move the air over the heatsink. Obviously, increasing airflow speed over a heatsink will increase the amount of heat that can be moved into the airstream which is why we use fans when needing to remove larger amounts of heat from a given volume.Conductive heat transfer is the ability of a material to move heat within itself. This is how heat gets from a chip to the heatsink (via the thermal paste acting as a bridge between the two materials). Aluminium is a worse conductive element than copper but silver is the best conductive element know to man. Ceramic space shuttle tiles would not be a good choice for a heatsink within our computersThe heatsink, be it ceramic or silver, is still limited by the rate at which it can reject heat from itself into the air via the convective process. This rate, in part, depends on the surface area of the heatsink, the rate of airflow, the ambient temperature (and the conductive coefficient of the heatsink itself). Increased heatsink area and increased air speed are the simplest ways to inceases the amount of heat one can reject into the airstream. This is why heatsinks are shapped like porcupines as the surface area with spikes is much much larger than a simple flat structure. But the biggest bang for buck is air speed which is why fans are so widely used (and silver is not).So, if you want greatest heatflow out of some chip, get a silver heatsink and the best thermal paste on offer (guess it would be silver metal based material) and push as much air over the heatsink that you can managed. At the end of the day, the air speed will make the biggest difference.However, since the RPi puts out a pittance of heat, it doesn't need any cooling beyong what can be handled via natural convection from the SOC area itself.In reality, a flat heatsink aound the size of the SOC made from silver (best conductive element known) or ceramic (unknown conductive coeficient) would be just like having no heatsink at all, since the convective heat transfere is related to SOC area and air speed over this area. So IMHO, you'd be buying a flat ceramic heatsink and thermal paste for no reason.By far, the biggest issue for RPi in a small case is that we can restrict the convective airflow which will redeuce the natural heat extraction from the SOC. In part, this is why many cases have slots around the GPIO pins and sides to let in cooler air while gaps around the top let the hot air out. Sometimes the conductive airflow can be minimised when connecting 40pin cable to GPOI as less cool air can get in which could result in higher SOC temps. Many have found that simply taking the top off in such situations is enoughAlternatively, either the case linked to earlier or the Kodi case, are both heatsinks in and of themselves. These case suck the heat from the SOC through the termal paste/pad using conduction but then radiate the heat from the case top into the air using natural convection. As the case top is more than 10 times the area of the SOC, it will be much much better at rejecting heat into the air as compared to some marginally larger (than the SOC) flat ceramic heatsink (which is inside a case and has the issues of airflow). Natural airflow over the case top case is more than in excess of what's needed to keep things cool with the only downside being using GPIO hats may not be able to be used within the case. Still, it's not needed from a cooling perspective but i like the Kodi case..As Klojum said, no need for need extra cooling solution even if moderately overclocked RPi