Reference for Menachot 48:1

מדרס ועשאו וילון טהור מן המדרס אבל טמא מגע מדרס

was used as a curtain, it becomes free of midras uncleanness<span class="x" onmousemove="('comment',' Since it is no longer intended to be used for any of the purposes (specified in the prec. n.) which make it susceptible to midras uncleanness.');">¹</span>

Jastrow