In Gilbert Raes’ report from his sample that was cut in 1973, he had noted the presence of cotton fibers in his sample.
It must be pointed out, however, that in some of the preparations from the warp as well as
from the weft of Piece I, traces of cotton fibers were observed. It would seem that the linen
threads had been spun where cotton had also been spun. The structure of these fibers was
examined to determine the type of the cotton.All the cotton fibers found in the linen yarn of Piece I, warp and weft, were of the Gossypium
herbaceum variety, the number of reversals being less than 10. It has sometimes been
remarked that these were superficial fibers having come upon the Shroud at times of the
numerous expositions. If this were the case, it is scarcely probable that all the cotton fibers
would be of the Gossypium herbaceum variety.
https://www.shroud.com/pdfs/ssi3839part3.pdf
https://debatingchristianity.com/forum/viewtopic.php?p=1113762#p1113762