Off jump I want to say the pressing comb.
However, now that I've had my first blowout since I started caring for my hair, I will say that my hair feels DRY as a desert since and I have noticed a lil' more breakage on my dry hair than usual. When I say 'more breakage' I mean by comparison to my usual braided/twisted or in some other type of PS which is not a fair comparison either.
I don't think I'm to crazy about the method my stylist used to blow my hair out using the blow dryer and a paddle brush. What stylist actually follows the tension method? It's just not operationally sound given the time it would take to get the hair dry and semi-straight.
When I remember getting my hair pressed as a child, I don't remember any hair being burnt and that hot comb used to be placed on hot coal. Coal to hair, hair to coal...And as for reverting, I wish I knew what heat damage was then, I might have been pressing e'ryday! Half j/k.
Lastly, the flat iron used in the salon is the same as the pressing comb IMO. They both emerge from a marcel stove, they both are metal and they both smoke. The comb untangles as it goes through your hair and the flat irons pulls down ripping out the hair as it moves along the shaft.
I tell ya, I still have no idea how I'm going to get my hair silky straight comes time for my big, BIG reveal when I'm WL. Since I have time, I'll keep the research going I guess....any thoughts?