The ablation of first surface materials by x rays is a primary threat to the final optics in the NIF target chamber. To meet the operational goals of the facility, the designs of the chamber wall, target holder, and diagnostic surfaces must minimize ablation by x rays, typically by specifying materials that are low-Z, high temperature resistant, and shock resistant. Additionally, the response of the optics to direct target emissions must be understood. This paper describes some experimental and modeling work to develop the validated computer models necessary to quantify the x-ray response of various materials. These codes and further experiments will then confirm the ability of NIF first surface designs to meet functional requirements.