Which innovative packaging design feature was first introduced for religious texts in the 1960s that revolutionized their portability and accessibility?

Throughout history, religious texts have been packaged and presented in ways that reflect their sacred status. From ancient scrolls to modern digital formats, the packaging of religious texts has evolved dramatically while attempting to preserve their sanctity. This trivia question explores an interesting aspect of how religious texts are packaged and marketed in the modern era, balancing tradition with accessibility.

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Synthetic leather covers with gold leaf imprinting that simulated traditional bindings at lower cost
The 'Bible paper' innovation - ultra-thin pages with special opacity treatment allowing for complete texts in compact form
Color-coded edge marking system for quick reference to different books or sections
Dual-language parallel text formatting with original language and translation side-by-side