Laser etching with a bridge laser is a process by which the laser does not cut all the way through the fabric. This is controlled by laser power and velocity. The faster the laser travels, the less it will cut. Laser etching creates a unique effect, which is also very profitable. There is no cost of materials with laser etching: no thread, no backing, no bobbin, no appliqué material is needed.
When it comes to cutting, just about any material will suffice. The laser can cut through single or multiple layers of materials. With etching, the material needs to be something that will not burn. Most synthetic materials such as polyester or fleece work well with etching. The thicker the material, the easier it is to do a nice, deep etch. Polyester performance shirts also etch well, but etching is subtler. If the etching goes too deep, it can compromise the integrity of the material. Etching is also at the mercy of the color that is revealed once the material is etched. Thus, different materials and colors should be tested prior to determining good candidates for etching.
Source: Ed Levy