There are going to be three of these now. I’m not sorry.
Seriously, the hats are important. They use their hats as umbrellas, when it rains on them. It rains on them a lot. I don’t know if that’s a Prague thing or if the directors are all very enthusiastic about wet Musketeers.
Each of the Musketeers has a special relationship with his hat. Athos uses his largely for slouching and hiding his feelings, and on one very memorable occasion, faked his own death for half an episode simply by pushing his hat a little further down his face. Aramis’ hat has a long enough brim that he regularly uses it to keep smoke and powder out of his eyes when shooting his musket. Porthos’ hat is larger and fancier than anyone else’s, just like his pretty armour.
D’Artagnan has no hat. That pretty much sums up his relationship to the rest of the Musketeers. He wants to be them, because they are older and better at everything, and they all have really great hats. He is occasionally allowed to borrow hats for comedy and espionage purposes, but otherwise… no hats for you, kid!
Sometimes, the hats are metaphorical.
There are spoilers in these episode reviews. The better the episode, the more spoilery I get. Read with caution, or just watch the show already.