From the description on the pattern page:

Just in time for the super cold weather, here’s a cap that’ll hold your small music player with no visible cords. And if you have a classic iPod or something larger, there is a port in the back that will allow you to thread your earphones through. If you do this, you can easily stow your music player in a pants or jacket pocket.

It’s great for working out out of doors, or just plain doing your thing on the streets of whatever city.

Knit from the top down for best fit, the Tune Cap takes between 200 and 240 yards of worsted weight wool. Superwash or not is up to you. It’s also a good idea to knit it for a snug fit. You wouldn’t want your music player to come flying out should you decide to do an impromptu Grand Jete or cartwheel.