Perhaps you want to custom some environment- friendly fabric bags. But you are confused which one is better, the canvas tote bags or the cotton ones.
Actually they are the one thing. The fabric which is weaved by cotton is called cotton fabric, it is one of the widely used material in the world. Cotton fabric is a collective name, covering a series of types.

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Generally we call it cotton fabric when it is six ounce per sqm, when the weight reach 8-12 ounce, we call it canvas fabric. Canvas got its name as it was used to made sails in the early times. They are both soft, breathable, comfortable and eco-friendly.
Canvas is made with a simple plain weave pattern of “over one, under one”, different from twill. The weaving yarns are two or more and thicker than the waving yarns of cotton. While the weaving yarn of cotton is only one.
When making shopping totes, the canvas is more widely used than cotton, as canvas tote bags are more durable than the cotton tote bags.

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Both canvas tote bags and cotton tote bags can be printed many colors.
The images on the canvas are more vibrant and vivid than those on the cotton bags.
The thin cotton fabric (less than six ounce per sqm)looks similar to liner, ivory color, can be seen-through, a little low quality.
The cotton tote bags can be coated for durability. The small cotton fabric bags can be made into drawstring bags, while the canvas tote bags can not as they are hard to drawstring.

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Both of them can be customized with various decorative finishing processes like silk screen printing, heat-transfering and embroidery.
If you want to custom fabric bags to hold heavy items, canvas tote bags is a good choice, if you want store some gadget, perhaps you can choose cotton bags, as they are relatively cheap.