User blog comment:Xilinoc/Ch. 545 - Blue Stripes/@comment-6904925-20130709150928/@comment-11051098-20130711153704

Yamamoto was furious when Kenpachi, Byakuya and Shunsui lost their haori during the battle against Aizen and the Espada, and didn't even care about it.

I think he said something, at least in the anime, about what the captain's haori represents. I take it that the haori represents the Gotei 13, and for each of the captains, represents their division, carrying the divisions insignia on the back.