Method for inserting out-of-plane reinforcement threads and method for producing fiber-containing material

A method for inserting out-of-plane reinforcement threads comprising:

• a preparation step of preparing a base material including reinforcement fibers that extend in a direction along a plane and providing a protective sheet on at least one surface of the base material;
• an out-of-plane reinforcement thread insertion step of inserting the out-of-plane reinforcement threads into an inside of the prepared base material and an inside of the prepared protective sheet only in a direction intersecting the direction along the plane;
• and
• a sheet removal step of removing the protective sheet after the out-of-plane reinforcement thread insertion step,
• wherein a length, protruding from the base material, of the out-of-plane reinforcement threads that are inserted into the base material is controlled by controlling a thickness of the protective sheet in the preparation step.