This line of swimwear is called Mezal (after the twins) and is starting to gain popularity not only in the twins' home in UK, but overseas as well. Oh and the Mezal swimwear isn't exclusive to Muslim women only - the twins claim that a lot of women have to cover their bodies due to religious, cultural and even medical reasons. With this in mind, Mezal comes handy because it allows women to enjoy swimming without the hassles of wearing big shirts, leggings and the like.
You can visit Mezal to check out their other designs.