Abstract: A base panel member 22 is provided with openings 24. A back panel member 26 having projections 28 that can be inserted into the openings 24. Springs 38 bias the projections 28 against the openings 24. Shape-memory members 40 are disposed in the vicinity of the springs 38. The projections 28 are inserted into the openings 24 by a biasing force of the springs 38, so that airflow through the openings 24 is prohibited. The shape-memory members 40 change shape according to temperature changes, and produce a force against the biasing force. This allows the projections 28 to be separated from the openings 24, creating an airflow state in which the air can pass through the openings 24. A design is formed by combining the base panel member 22 and the projections 28, while the projections 28 are inserted into the openings 24.