Light blue blocks are light blue squares, hence the name, and have rounded corners. When extended, a grey-blue screw is also seen holding the block. Gears can be seen in the cavity where the block was.
Light blue blocks will remain shut until the player presses a blue switch, at which point they will move forward or backward, depending on their position, to open or close access to certain areas. They have to be opened to complete levels, and can kill Norman Noggin if he gets squished.
A closed blue block, before being opened by a switch