I get a lot of questions from folks who are new to the world of LEDs asking what kind of diffusion materials are best for NeoPixels or other addressable LED projects. This isn’t just a newbie question either: LED Electronics makers are constantly searching for new ideas about diffusion. Every project is different, and there are so many material choices available. The products range from really cheap to super expensive, and it can be hard to tell which materials are worth the price, and if there are less expensive ones that will do just as good a job.
I just published a tutorial and reference guide about LED diffusion over on the Adafruit Learning System. It covers a lot of different materials including a lot of different fabrics, papers, fancy LED foams and plastics and basic household items. I set up a board with a lot of different pixel density strips: LED dots, 144/m NeoPixels and lower 60/m and 30/m strips, and tried a whole bunch of diffusion materials to see what looked best.
My favorites: In the fabric category, I really loved the look of white fun fur. It can be fairly expensive for the nice stuff, but you can also find cheaper varieties at fabric stores or online.
In the plastic category, I loved the look of black LED acrylic. This stuff is fairly expensive as acrylics go, but it’s made specifically for diffusing LEDs and gives a really nice sharp look while still diffusing and softening the pixel lights.
In the foam category I really liked the look of the LED foam. This is a closed-cell foam that’s specifically made for diffusing LEDs. It’s pretty expensive, but did a really great job of diffusion! For a smaller project this stuff seems worth the price tag.
Product links and video clips of all the different materials can be seen here: https://learn.adafruit.com/make-it-glow-neopixel-and-led-diffusion-tips-tricks