Dear,
I just came across this site out of curiosity, read your post and thought I should still post this answer. Even though the question you posted was not current in this case it is still not too late to get you the answer you so desire to learn. So here it goes. According to a piece I read by Dr. Harris,( His Eminent ) the late Mr. Edgar Cayce in his instructions mentioned about why he recommended wool for Castro oil application was because, 'He (late Mr. Cayce) said that white wool flannel has the needed electrical and conductive properties'.
Hope this answer will benefit you and those others, and wish you all the best on your journey to healing whatever that may be. Toss to fast and permanent recovery!