@ Zakalwe, it's not really the seam it's how the fabric gets stretched. My experience the arm and leg warmers that are made like socks with no seams have better compression the whole length of the arm or leg. Were as the seamed one always have gaps and didn't stretch back... I will admit that I haven't used any of the "newer seam ones".
Kinda like a chinese finger trap vs as shirt sleeve
@ sugarcane The defeet makes both wool and synthetic and I was going to say my pair are older than Rapha been in business but that isn't fair and I can't remember when I bought them but it's close to 8 to 10 years would be my guess. My synthetic ones lasted 12 years before I had to replace them.
I live in NorCal so I use then 2/3 of the year riding a little when the sun isn't up and in the winter when it's "cold" : )
PS The guys I ride with started using swiftwick ones but they only make synthetic and you need the wool when it get close to freezing.https://www.swiftwick.com/subcategory_51.htm