Freezer paper stencils are a quick-and-dirty alternative to silkscreening, since you don't have to wait for a screen to dry or develop, and freezer paper can be purchased cheaply at just about any grocery store. However, cutting out a stencil by hand can be quite tedious, especially with a highly detailed design. If you have access to a laser cutter, you can put the x-acto knife away and save yourself quite a bit of time!

Materials:

Fabric
Fabric Paint (I used Speedball Fabric Screen Printing Ink)
Freezer Paper
Sponge brush and/or paintbrush
Iron and ironing board
Laser Cutter (Ah, there's the tricky part if you don't happen to have access to a laser cutter. I made it at TechShop with the Epilog 60W laser cutter)

Step 1: Design or Download Your Stencil

I made my stencils in Inkscape, saved as a .PDF and imported into Corel Draw (Inkscape doesn't always output to the laser cutter in predictable ways...)

You might want to add reinforcement bars if your design has a lot of "islands" or "peninsulas," i.e. areas which will fall out or will be flimsy after the design is cut out.

*Extremely* fine detail might not come out clearly in your finished print, especially if you are working with a coarse fabric.

My speed/power/frequency settings to cut the freezer paper were 70/40/500 on the Epilog 60W laser cutter, and I suspect that this was overpowered. Your optimal settings may vary.

The freezer paper will tend to flutter and curl as the laser cutter runs if you do not weight down the corners of the paper.

Step 2: Iron Your Stencil Onto Fabric

Use a medium heat iron to adhere the freezer paper to your fabric.

Important:
Iron the paper onto the fabric with the *shiny side down.* Otherwise, the stencil will not stick to your fabric, and, if you don't use a press cloth, your stencil will melt onto the iron.

Step 3: Apply Paint

Use a sponge brush or paintbrush to fill in your stencil. A straight up-and-down daubing movement with the brush provides the most crisp results.

When the paint has dried, peel back the stencil. If your particular fabric paint requires heat setting, iron again according to the manufacturer's instructions.