I have an opinion -- it's only an opinion -- so throw my opinion away if you want. The mattress pad will work for a simple quilt which does not have hours and hours of work, and you have not invested in pricey fabrics to make a beautiful quilt top. If the quilt is utilitarian in nature, and will be drug through dirt or sand on a beach, or grass stained in the park -- yes, go for it. Use the mattress pad for the batting. And it will service you for years! But...but...if you are investing in making a thing of beauty with gorgeously chosen fabrics, and skill in piecing, and it can possibly become a family heirloom....draw the line here. Don't use the mattress pad instead of batting at this point, and cheapen your project. So, the question is really: "What is the purpose of the quilt?" That's just an opinion.