Numerical control boring and routing machines use curtains made from resistant, but flexible materials to protect end-users from the projection of wood chips and tool pieces. These curtains allow the work piece to gently pass through, but firmly stop every small sharp piece or fragment ejected at the highest speed by fast drilling tools. Nowadays, curtains are commonly made in flexible thermoplastic materials as polyamide, polyurethane, polyvinyl chloride or similar materials. Safety issues to be addressed related to the risk of projection of parts during processing are defined by EN 847-1 and EN 847-2 standards, both collecting practical experiences from manufacturers and users. The effectiveness of these curtains was investigated by technical observations, experiments and even numerical simulations, but conclusive results are not available at the moment. This independent research, where ballistic impacts on flexible curtains were simulated using finite element (FE) methods, aims at verifying the effectiveness of specific protective barriers when realized and used in accordance with the UNI EN 848-3 standard. Numerical simulations were permitted to verify the congruity of the main barrier’s characteristics (materials, shape, depth, mass, cost, etc.) in relation to the projectile parameters (shape, mass, speed, direction, etc.) identifying their mutual influence. Outcomes from this research provide useful information toward the definition of a new way for the design of efficient curtains. A comparison between numerical simulations and experimental results coming from ballistic tests was also realized, permitting to validate this predictive methodology.