If you have any of the Air models which lack fans, there's a common hack of putting thermal pads between the CPU heatspreader and case, effectively turning the bottom case into a large heatsink, and giving your system a longer maximum performance before throttling.
The downsides is that this makes the bottom of the case quite hot on a place you can touch, but putting a plastic hardshell over the entire laptop deals with that, and also gives protection.
The downsides is that this makes the bottom of the case quite hot on a place you can touch, but putting a plastic hardshell over the entire laptop deals with that, and also gives protection.