Alder with or without space for USB.
The best storage for a photo book is at about 43% humidity.
If you have too low or too high humidity, the pages in the book can bend,
which is natural but not desired.
It is primarily the first and last sheet that bends slightly, These blades are a combination of different materials that react differently to humidity.
But it's no cause for concern, put the book in a room with a better humidity,
and placing another book on top as a little weight to even out the book's own humidity within a few days. P>