Beautiful, Mel. The two protective sheets that ship with snapframes are common plastic; no acid-free or uv qualities.
Just for clarity of terminology for anyone interested: Pepsi is a brand of soda. Plexiglass is a brand of acrylic.
Variations of acrylic are endless but they can all be called thermoplastics, or by it's chemical name, methyl methacrylate, which is more commonly called "acrylic". Once that's understood you can narrow acrylics down to commercial brand's like Lucite, Acrylite, Polycast, Oroglass, Lexan and of course Plexiglass. Different acrylic manufacturers boast different strengths but Plexiglass brand acrylic is what most framers use. Glass sucks for a lot of reasons.