The Enforcement Rules of the Prison Act Article 39

The supervisory authority shall determine the colors and styles of the outfits that prisoners are obliged to wear in accordance with Article 20; and the outfits shall meet sanitary and health requirements by using materials that satisfy cooling, ventilation or warmth requirements.If required due to temperature or health, with Prisons’ approvals, prisoners may use their own clothes, hats, socks, beddings and proper warmth-keeping objects or those sent to them.
中文原文 監獄行刑法施行細則第39條
依第二十條規定受刑人所須穿著之外衣,其顏色、式樣,由監督機關定之;並基於衛生保健需求,採用涼爽透氣或符合保暖所需之質料。
因應氣溫或保健上有必要者,經監獄許可,受刑人得使用自備或送入之衣類、帽、襪、寢具及適當之保暖用品。

English translation for reference only; the Chinese text prevails. Not legal advice.