I use materials that I have on hand, and sometimes I continue with a theme that I'm working on at the time. Because I make two dozen or more, I don't want them to be too complicated.
This year, I began with hand-dyed cotton, and used a stencil with pearlescent acrylic paint for the tree. The cotton was backed with batting before being machine stitched with silver thread to emphasize the lines of the tree. Then I heat-fixed some crystals onto the surface.
I used a heavy watercolour paper for the third layer, and zigzag stitched the perimeter with the silver thread.
They are reasonably stiff, enough to weather their trip, and the paper will easily accept my scribbled greeting and address.
The Tuscan-themed edition of 2011 had no stitching other than the edge finish, but featured image transfer and multiple stamping on hand-painted cotton. I used a heavyweight interfacing for this one: because there was no quilting, there was no advantage to using batting.
The 2010 special was an extension of my Love, Love, Love theme. It had a Victorian feel, complete with antique buttons, pearls and lace and vintage-style photos. This version was a little too thick to pass the test for thinness at the post office, but once it was sheathed in a plastic wrapper, it was a go.
Of course it's too early for seasonal greetings, but it is satisfying to know I have a little stack all made and ready for their journey.