I googled around and there are mask patterns everywhere. I found one I liked with a nifty filter area but it wasn't comfortable. I found another but it had no filter. So I took the two ideas and I put them together to make a comfy mask that also has an opening type pocket for placing a filter. Here is the link to the free pattern that I used, it is available at Eat Pray Create.
Aslo, I tried this with heavy material and discovered that using lighter weight material works better, so I used a t-shirt and a bandana.
Here is how I made it:
I cut the tee shirt into two 8x12 pieces. And on the 12 inch side, smack dab in the middle of that 12 inches I sewed straight toward the center of the rectangle for approximately 2-3 inches, then left some space and sewed another 2-3 inches to the opposite side.