Think of a colouring book, but made of fabric and big enough to cover your lap on the sofa. 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.
What makes the difference is the washable ink. According to the manufacturer, washable water-based ink comes out in a normal wash, leaving the printed outlines ready for another round. The care label sets the temperature and drying.
Permanent fabric pens are for the reverse: a design you want to keep, which will not wash out. It helps to decide before you start which parts should be permanent.
Some simple habits make it easier. Pull the fabric flat on the table and cap each pen as soon as you put it down. 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. And once coloured, it is still a cosy throw for the sofa.