Plastic Flips are available in various materials. "Soft" flips were once made from polyvinyl chloride (PVC) which decomposed over time with disastrous results for coins; leaving a green appearance and substance. PVC flips are no longer made and sold. Mylar, vinyl and acetate flips do not contain PVC. While not airtight, they are reasonable choices for moderate value coins that will be "left alone" for multiple years.
Vinyl Pages (8 ½ x 11) which fit into a 3 ring binder. Well suited for Cardboard and Vinyl Flips, with great visability of coin obverse and reverse. This is a Great Favorite.
Mylar-lined Cardboard Flips, often called "2x2s" or cardboard flips. At one time, the most preferred and commonly used. but also available in other sizes, are similar to plastic flips. A coin is placed between the two halves, which are then folded over and stapled together (some brands contain an adhesive). The boxes that they come in are ideal for multiple coin storage.