I am aware they are OK, but a woolen or 'Beenie' hat is what I am talking about...Don't think so, but not 100%.
In a related story, was on my first county cup game today. Just after kick-off I look round and a player has a hat on! I wait until the ball goes out of play, run over to him and say "Get that hat off please." He replies "Are you serious? I fractured my skull!"
I then realise that its a protective one (like Cech wears for Chelsea).
"Sorry buddy"
The law doesn't explicitly state that they're not allowed, but it also doesn't say that they are.
I've just had a look at the FA and FIFA laws and both state that items can be worn in addition to the basic equipment (shirts, shorts, shin pads, boots etc) as long as they are not deemed by the referee to endanger the safety of the wearer or their opponent.
I'd probably allow a hat to be worn based on the fact it isn't really dangerous (It's likely to just come off if pulled etc).
If it is soft and woolly then no problem for me, not that I often see it.
Would your opinion change for goalkeepers wearing caps due to sun?
Is it dangerous?