secondary material; subsidiary material
Refers to materials that support or supplement primary materials in manufacturing, construction, or other processes. Often used in technical or business contexts.
We use recycled plastic as a secondary material for this product.
Reducing the cost of subsidiary materials significantly affects overall profits.
Compound of 副 (ふく, 'secondary, auxiliary') and 資材 (しざい, 'materials, resources'). The term is a modern technical coinage.