The Sash skins can go up to +25
The minimum level to use a sash skin is 105
You can add up to 5 bonus to your sash skin and those bonus are not removable
You can switch the bonus that you choose with Sash Skin Switcher
You can use Improvement Scroll (Sash Skin) to upgrade your sash, the sash can downgrade
You can use Improvement Stone (Sash Skin) to upgrade your sash, the sash cannot downgrade
From +0 to +9 your sash skin can have a limit of 1 bonus and that extra only goes up to 1 value (table below)
From +10 to +14 your sash skin can have a limit of 2 bonus and those extras go up to 2 value (table below)
From +15 to +19 your sash skin can have a limit of 3 bonus and those extras go up to 3 value (table below)
From +20 to +24 your sash skin can have a limit of 4 bonus and those extras go up to 4 value (table below)
At +25 your sash skin can have a limit of 5 bonus (Max) and those extras go up to 5 value (table below)