Buying someone a cap for Christmas is easy with a giftcard. The main obstacle with buying a cap for someone else is whether or not you know their headsize.
But with a giftcard, they can figure it out themselves! Then you don't need to guess or try to weirdly measure their head or caps they own to try and second guess.
Digital giftcards start at £20 and you can either pick the price based on what cap you suspect they will like, or you can pick the price based on how much you want to or can afford to spend. Giftcards are always a good option if they have always wanted a cap.. but they are out of their current price range. You don't need to buy the whole cap, just get a giftcard for half the price of a cap and help them by paying towards it. Sometimes £20 is more manageable than £45.
Digital giftcards are emailed straight to you too, so keep it in mind as a back up if you are still looking at all your options for someone, as they can be bought right up until christmas day and there's no need to rely on the post getting it to you in time.
For actual giftcards, and something literal to give to someone, postal giftcards come in multiple different colours for the envelope, so you can give them something pretty and aesthetically pleasing if that's their bag. Also just makes a nicer gift to give in a fancy envelope.
Giftcards are also available to order with or without a tape measure, so they can work out their headsize and order straight away on christmas day if they so please.
You can also pick the box colour for giftcards with a tape measure.
If you do want to work out their headsize and order someone a cap, don't forget that sizing info on how to work out a headsize is here.