Janice, there are many schools of thought as to what material is best for dust collection. The Amish use a special felt type material, there are engineered fabrics designed for filtration. Perhaps this is one of those situations where it is better to not try and re-invent the wheel? I would purchase one of the pre-made bags. This way you know for sure what level of filtration you have. Since the smallest particles are the most likely to get into your lungs these are what you are targeting.
"Living in the D" (this means Detroit!)
"It's fine to disagree with other members as long as you respect their opinions"