Arnold is always seen wearing his small blue hat.
Arnold's parents bought him his hat when he was just a baby (as seen in "The Journal") and he has worn it ever since.
In "Arnold's Hat" he is shown to be emotionally attatched to his hat, to the point of refusing to leave his room without it. Arnold is so attached to his hat because his parents gave it to him, and he still misses and loves them.
Times when Arnold is not wearing his hat
This category focuses on times when Arnold was wearing a different hat, his hat was covered, or he took it off.