Recently it has been even more improved, to feel even more heat and to maximize the 'efficiency of exhaust systems, especially in turbo engines, where these protections keep the heat in the tubes of the collectors, so the speed of the exhaust gas remains truly high and allows the exhaust gases have more energy when they encounter the vanes of the turbocharger.
This patch prevents the heat being dissipated to the surrounding components and the rest of the engine compartment.