It looks like an ordinary throw, except the design is printed as outlines that you colour in yourself. Most measure around 150 x 125 cm and come with a set of pens in the box.
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.
Themes range from flowers and fruit to cats and more fantastical scenes. Large areas fill quickly; small detailed zones take longer but look striking when finished.
The key detail is the ink. Washable pens use water-based ink that, per the manufacturer, washes out in the machine, so you can start again. Always follow the care label on the blanket.
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. Colour on a flat surface so the fabric does not stretch, and close the pens after each session so they do not dry out. Start with lighter colours; darker ones are easier to add than to take away.
For adults it is a calm, screen-free way to unwind in the evening, much like a mindful colouring book. It is also a popular Christmas gift idea, as it is still useful once the colouring is done.