A page protector looks like a plastic sleeve. Folded over from right to left and punched with holes in most cases at the left side and welded together along the hole line and at the bottom of the page. Leaving the top of the page open for easy insert of paper, photos and documents. They are available in different sizes and in different texture. Most are sold for storage of letter size (8-1/2 x 11) paper documents and comes with a reinforced hole line at the left side, pre-punched for a punch free storage solution with standard 3-ring binders. The reinforcement at the hole line side is often seen as a white strip but can also be seen as a clear strip or non at all if the holder is made in material thick enough where a reinforcement strip is not needed.
The most common sheet protector is made with only an opening at the top. This being a: Top Loading Page Protector but they are also sometimes available with an opening at the left side along the hole line side this being named a: Side Loading Page Protector.
The holders and pages are often used with scrapbooking projects and here it seem like a glass clear also called polished surface is preferred over non-glare material texture. In addition a heavy or super heavy gauge material is chosen over standard or economic gauge material the latter two simply can not carry the weight of modern designed scrap book page with all the extra designer add ones.