About every fourth person I speak with asks why the The Brew Bag is better than a paint straining bag, or why not just get the two pack nylon bag from their local home brew store, or why not just use a muslin bag, "that's what the steeping brew kits come with". So here's the straight up on bag material and why Voile is the best.
Paint strainer bags are made of nylon and have a thread count of 45. Thread count is measured in a square inch both vertically and horizontally. Paint strainer bags have 9 threads vertical and 5 threads horizontal, so 45 TPI (threads per inch). A paint straining bag is designed to remove chuncks of dried paint, or drywall paper that gets stuck to the roller, or if spraying, anything else that would otherwise impede the operation of the paint sprayer. Using a 5 mega pixel camera you can see in the photo below the thread count will allow grain and hop bits through the material. It will work, but it won't work as well. Granted the trub will settle out of the wort anyway, but why allow it in the wort at all? You can also see the tear in the fabric I made by simply pulling at opposite sides.
Muslin bags are typically what is supplied with "partial" grain extract kits. They work for that intended purpose, and they are considered disposable as they stretch, not only when used, (making the gaps in the thread bigger) but even after a washing as well. Muslin provides even less filtering capability than a nylon bag. And, yes, you can tear one apart very easily.
Depending on the country of origin and manufacturer, Voile has a TPI count of between 85 and 95. it is made of polyester, does not stretch, and is very strong. Due to the construction method and material used, a grown man can not tear it. We don't know how many brew sessions a voile bag will produce, but we've used ours over 50 sessions. At that rate a good voile bag costs $.71 per use. Paint strainer bags cost $6.50 for two five gallon bucket sized bags..and they will break down. If you have kettle bigger than the paint strainer, you're out of luck. Nylon bags come in various sizes and range in price from $14.00 to $2.99...and they will lose their thread alignment and burst at the seam under pressure.
There is another bag maker who instructs on his web site to not squeeze the bag as it puts undue pressure on the seams - which may cause a rupture. The Brew Bag ENCOURAGES squeezing of the bag - we know it will not rupture! Now compare the three images in this article and you'll see why The Brew Bag is as much a part of your brewing equipment as your kettle and why you should seek out Voile for your choice of material.