Outer wall material and method for manufacturing same

A method for manufacturing an outer wall material, the method comprising:

• a first step of heating and softening a glass material;
• a second step of molding the glass material softened in the first step to form first and second bottomed containers, each of the first and second bottomed containers including a bottom wall, a side wall, and a upper portion being open;
• a third step of combining the first and second bottomed containers obtained through the second step so that the upper portions face each other;
• and
• a fourth step of forming a reflection member by applying a coating to an outer surface of the side wall of at least the first bottomed container of the integrated first and second bottomed containers,
• wherein in the second step, a prism portion is formed when the first bottomed container is molded, the prism portion causing the reflection member to collect light incident on the prism portion at a first angle with respect to a normal line of the bottom wall that is equal to or greater than a predetermined angle and to retro-reflect the collected light, and transmitting light incident on the prism portion at a second angle with respect to the normal line of the bottom wall that is less than the predetermined angle, and
• the first and second bottomed containers are maintained at a temperature exceeding an annealing point of the glass material in the second step and the third step, and are lowered to a room temperature between the third step and the fourth step.