Date: 8 Adar 5562
From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer investigates whether silk, derived from non-kosher silkworms, may be used for synagogue furnishings and Sefer Torah accessories given the principle of min ha-mutar b'fikha. He tentatively permits silk for synagogue items based on multiple leniencies, but for tashmishei kedushah like Sefer Torah threads, he requires the silk to be permanently dyed to constitute a genuine halachic transformation.
Source: Shu"t Chasam Sofer OC §39