It does what it sounds like.

ITEMS:

SHIRTS!

They're just worse leather armor, but blue always. they cost 6 leather and 3 light blue dye (TOTAL, actual recipie is 2 sleeves 2 leather 1 light blue dye.)

SLEEVES!

Ingredient in shirts. 2 leather, 1 light blue dye.

ICONS?

Does nothing and is unobtainable w/o commands.

ADVANCEMENT!

Shirts & Sleeves

The very real 1.22 update (Not obtainable, Might patch sometime.)