It's been awhile but I think I'm remembering poplin being a little heavier weight or more tightly woven such as can be used for summer shorts. I don't think I'd want to use it for the applique pieces but it would be ok to use for a background block since actually anything can go into a quilt as long as it pleases the quilter. This is why it's good to be actually touch fabric when shopping for it. You can see or feel the weight before purchase to see if it's what you want to work with.