The wet towel method is a cross between wet blocking and steam blocking. You pin the piece to size, lay a damp towel over it and press the towel with a hot iron, so steam is forced through the fabric without the iron touching it.
Use it when you have no steam iron, or when the fiber should not have direct heat on it. It works especially well on edges that curl. It makes a lot of heat, so do not use it on acrylic, which melts, or on cotton, which shrinks.
If the finished piece sets with a lip along an edge, steam it a little more and pin more often along that edge, or do not stretch it quite so far.
1 Measure the piece
Lay the piece on the blocking mat and measure it. Here it is curled and a little under six inches, and the aim is a bit over six.
2 Pin it to size
Pin one corner with a T pin, then stretch the piece to the measurement you want and pin the other corner.
3 Pin all the way round
Work along each edge, keeping it even, and stretch both ways so the piece meets the measurements on your schematic. If the sides curl, pin them too, so the fabric lies flat.
4 Lay a damp towel over it
Soak a towel, squeeze out most of the water so it is more than damp, and spread it over the whole piece.
5 Press with a hot iron
Set the iron to a temperature that suits your fiber and press the towel. The heat turns the water in the towel to steam and forces it through the fabric. Keep going for a little while. Not for acrylic, which melts, or cotton, which shrinks.
6 Lift the towel and let it dry
Take the towel off and leave the piece pinned. It is hot and damp, so let it air dry before you touch it.
7 Unpin and check
Pull the pins and look. The steam has set the stitches and the fabric lies flat with no curl. If an edge set with a lip, steam it a little longer and pin more often along it, or stretch it a little less.