From the manufacturer:
These value-priced, super value packs of canvas panels are great for lighter paint applications, quick studies, practice and class projects. The unbleached 3 oz. cotton is primed with acid-free acrylic titanium gesso to a finished weight of 8 oz. and is wrapped around an acid-free recycled paper board core. Suitable for use with all acrylic paints, oil paints and other wet or dry media. The number of panels per pack varies by size.