Jabba notes that according to John Lupia writing a comment in this blog:
Gilbert Raes published several times that the linen threads of the main cloth of the Shroud of Turin contain traces of cotton fibers since the linen was spun in context with cotton at the time the threads were manufactured. Consequently, on authentic specimens of the Shroud of Turin used to test we expect to find linen and cotton, and the cotton is not a rogue fiber but one that should be found as per Raes.
Jabba adds, “This is pretty damning. Is it true?”