Purity: Objects Purified or Not Purified by the Sun
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 186
The sun can purify an impure ḥaṣīr mat; but if it is woven with thread, the sun does not purify the threads. Furthermore, based on obligatory precaution, trees, grass, doors, and windows do not become pure by means of the sun.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)