Which type of materials must be stacked and blocked to prevent spreading or tilting?

Cylindrical materials must be stacked and blocked to prevent spreading or tilting because their shape inherently makes them more unstable when placed in a stacked formation. Unlike flat or rectangular materials, cylindrical items have a curved surface that can easily roll or shift if not properly secured. As a result, when storing or transporting cylindrical materials, it is crucial to use blocking or bracing techniques to maintain stability and ensure safety. This helps to prevent accidents and allows for more efficient use of space while handling such materials. In contrast, flat, triangular, and rectangular items tend to have more stable stacking properties, reducing the risk associated with their arrangement.