Sometimes, the world of duck can be confusing. Who knew that one type of 100% cotton fabric could have so many variations, before you even add color? Sometimes duck is referred to by its weight (such as 10 oz duck) or sometimes it's assigned a number, such as this #4 duck. This is known as, unsurprisingly, a 'number' duck. The number does indicate the weight, but not directly. #4 duck doesn't weigh four ounces. It actually weighs 24 ounces per square yard. The lower the number on a number duck, the heavier the fabric will be. You can choose the perfect duck for any project by making sure you have the right type for your needs. #4 cotton duck is most commonly used for things like farm or military applications, like feed bags or saddle bags, or heavy duty equipment covers. It is heavy and rather stiff, and is undyed and unbleached.