The bookmark patterns are designed to fit on a card 50 mm x 152 mm (2 ins x 6 ins). This is half the width of a standard double fold card so it enables them to be used as bookmarks or greetings cards.
If you cut a single panel from a standard paper embroidery greeting card and fold it in half this will be the basis for the bookmark. When the stitching is complete you can close the card to hide the back of the work.
A UK mail-order company called Craft Creations sell ready cut bookmark blanks that measure 50 mm x 179 mm (2 ins x 7 ins). They are single sheets of card so you would need two for each bookmark – one to cover the work on the back. They also sell envelopes to fit the bookmarks and clear polypropylene bags made to fit the bookmarks with an envelope.
If you put “clear bookmark covers” into a search engine it will come up with a number of places to get them. Add your country to refine the search.
Another possibility is “transparent self adhesive film”. This is often sold in office supplies shops for covering books.
If you are doing a lot you might consider a “laminator” machine. I have seen them advertised from under £30 in Staples office supplies.
See our Useful Links page for equipment and materials suppliers.