Pictured are a solid barrel iron called a "marcel iron" as well as a hollow barrel iron called a "Bumper" iron. I believe the solid barrel iron holds heat longer than the hollow barrel iron. Although, the hollow barrel iron heats up faster in the stove.
I have seen some online video showing Kizure irons being hollow barrel. Golden Supreme irons are usually solid barrel. Pictured is Kentucky Maid product offerings. Their irons do not come pre-tempered. Notice the emphasis on hollow barrel and solid barrel. They define solid barrel as "marcel" and hollow barrel as "bumper." There always seems to be more to learn.
Do you remember Jason Griggers from the "Good Hair" movie? He was using marcel irons when the cameras came to his salon to interview him behind the scenes for the hair battle. Recently, he started styling for FHI Heat as a platform artist at Bronner Brothers hair show 2010. Please see my separate article highlighting FHI Heat instructions. I am going to watch his career as he transitions into more flat iron usage. I really do not think that this is a healthy direction, but we all have gotten that "flat iron" fever at one time or another!