Your quilt top is done (hooray!) and it's time to pick the middle layer for your quilt sandwich-- batting! With so many options out there, choosing the right one for your quilt can be overwhelming. It's great if you already have a favorite, but knowing how different batting weights and fibers affect the look and feel of the quilt can make a big difference in your next project. Let's take a look at the most popular varieties.
Cotton batting is made from natural cotton fibers, sometimes bleached and sometimes not, and is typically thinner and more dense (it has very little loft) than polyester or wool. Cotton batting is a popular choice for quilts that will be used in multiple seasons, as cotton isn't too warm for summer, and is also popular for heirloom quilts that will be stored and used for many years. Cotton has the benefit of being the same fiber as quilting fabric, meaning it will wash nicely, though can suffer some shrinkage. Since cotton batting is thinner and not as puffy as other fibers, it doesn't always "fill out" wide spaces between quilting stitches, making for more crinkly quilts after washing, which can be a benefit or a disadvantage depending on the look you want.
Cotton is sometimes blended with other fibers such as polyester (which lightens it and reduces shrinkage) or bamboo, silk, or wool for added warmth.
If you're looking to make your quilt both puffy and warm, wool batting is for you! Wool has a high, springy loft and makes quilts surprisingly light. Made from processed and combed sheep's wool, wool batting is an excellent insulator making for warm quilts with longevity. You'll want to make certain to only gently wash your wool batted quilts in cold water, as wool has a tendency to felt under agitation and heat (and it may smell a little "sheepy" during the first wash-- no worries, it will be gone once it's dry.) Wool batting's high loft makes for excellent stitch definition in your quilting, making it perfect for closely placed quilting, and looks pleasantly puffy if you choose sparse quilting. Wool is sometimes blended with cotton, silk, or bamboo for added qualities.
Polyester batting is a man made synthetic fiber and is most often what's found in mass produced duvet covers and quilts due to it's low cost and ability to make quilts both light and puffy with variable lofts (it can be as thin or thick as desired and comes in multiple lofts.) It's also reasonably comfortable in a variety of climates, being warm or cool depending on said loft and doesn't shrink. While these are qualities that are desirable, polyester is not very durable due to the loosely connected fibers in the batt and has the tendency to break and clump inside the quilt with subsequent washings. Polyester batting is still an ok choice for some quilts, but is often better blended with cotton or wool to make it more durable.