I dont know the weight of the canvas i use, i go to the store and check it out by feel. I have used thinner material, really thick and now use a medium weight. Once layered the belts are still light weight and flexible but strong enough to hold blasters and pouches.
Here is a picture of the canvas i use, it can also be known as cotton drill, which is the weave or pattern and i use both natural and white canvas depending on the costumers preference.