A radiatively cooling substrate and a manufacturing method thereof are provided. The radiatively cooling substrate includes a metal substrate and a chitosan layer disposed on the metal substrate and having a thickness of  0.5 m to 10 m ; wherein the chitosan layer emits radiation with a wavelength between 8 m to 13 m.

1.此散熱塗層可施作在任意形狀、大小之金屬基板上。
2.散熱效率雖受大氣、日照與環境溫度影響，但日間與夜間均能散熱。
3.塗層材料取材天然，環保、無毒且生物相容，價格也便宜。
4.以輻射方式將熱(波段 8 m – 13 m為主之中紅外光)通過大氣層散失在外太空， 無需輸入能源或動件運作。

The invention can be applied as auxiliary means of heat dissipation to outdoor fields objects such as general containers, refrigerated containers, metal houses, transportation vehicles, metal pipelines and metal storage tanks. The energy consumption and cost required for heat dissipation are reduced.