By default, your TravelMap book will be printed with a softcover, the most common way to bind photo books.
You can choose to print your books with a hardcover instead which thicker and more expensive.
EDIT: all book are now printed with a hardcover by default

You can choose the cover type after clicking on the button "Print / Download" on the preview page.
Note: you'll need to have at least 32 pages to select a softcover.