It looks like an ordinary throw, except the design is printed as outlines that you colour in yourself. Many come in at about 150 x 125 cm, with their own set of pens.
The design is large, so it works best a little at a time rather than in one sitting. It is one of the few hobbies a whole household can share on the same piece.
Many designs are printed as white outlines on a black background, which gives a stained-glass look once coloured. Choosing the design is half the fun, so it is worth looking at the whole pattern first.
The key detail is the ink. According to the manufacturer, washable water-based ink comes out in a normal wash, leaving the printed outlines ready for another round. Check the care label before the first wash.
Some people switch to permanent pens for a finished blanket they want to keep as it is. You can mix both on the same project, as long as you remember which parts will stay.
Two small tips before you start. Lay the blanket flat on a table rather than on your knees, and put the caps back on the pens between sessions. Start with lighter colours; darker ones are easier to add than to take away.
It is an easy way to keep your hands busy while chatting or listening to music. As a gift, it suits people who love crafts but already own plenty of colouring books.