Most manuals recommend the use of cut-away stabilizer for embroidering knitted fabrics, because this type of stabilizer remains between the finished embroidery and the fabric and helps the textile keep its shape.
On the one hand, photo-stitch designs deform knitted fabric easily and one layer of cut-away stabilizer is not enough. On the other they are very dense by themselves and if you use several layers of stabilizer, your sweatshirt will resemble a piece of medieval armor and will probably be bullet-proof. Although these can favorable qualities, they don't add much to the look of the clothing.
Therefore, we recommend one layer of very fine cut-away stabilizer, or organza, and several layers of water-soluble stabilizer. We recommend Sulky's Ultra Solvy, which is very tough, for backing and Sulky's Solvy, thinner, for topping.
The drawback to this method is that you'll have to put your brand new sweat-shirt into a bowl of cold water for a couple of hours after finishing the embroidery. However, we didn't find the water particularly damaging.
Step One (the most important one!): Get a plain sweatshirt and place it on an even surface. We picked ours up at Sears for under $15. Mark the area where you want the embroidery with a washable marker. Take a piece of water-soluble stabilizer and cover it with a piece of organza or cut-away stabilizer. We chose the design Snowman Couple.
You can "glue" both stabilizers together by moisturing the water-soluble one a little bit. Place both stabilizers on the wrong side of the sweater under the area that needs to be embroidered. On top, cover the area to be embroidered with another piece of water-soluble stabilizer. Hoop.
Step Two: Let your machine fulfill the embroidery. Remember to cut away all jump stitches after every color!
Step Three: After finishing the embroidery, cut away all the excess stabilizer. It is especially important to cut away Sulky's Ultra Solvy as close to the embroidery as possible because this stabilizer gives a dense glue-like mess when moistened. So get rid of as much of it as possible before placing your sweat-shirt into water.
Step Four: Place your sweat-shirt into a bowl of water for a couple of hours. Rinse. Lightly wring out and leave to air dry on a towel.
You can see the result of our efforts on the photos below:
This sweatshirt features the design Snowman Family.
This boy's sweatshirt is decorated with his favorite dog: a Cocker Spaniel.
Kitty Got his Christmas Gifts adorns the front of this plain gray sweatshirt.
See also other photo stitch on clothes projects: Denim Jacket Decorated with Photo Stitch Embroidery, Jeans Jacket, Shirts with Photo Stitch Embroidery.