This study concerns concrete manipulatives for use in mathematics education, specifically in the realm of negative numbers and the operations on them. The author presents a review of relevant theory, practice, and research and develops guidelines regarding characteristics of manipulative materials. He concludes that present practice in teaching negative numbers does not use materials that meet the implications of theory. The study continues with an examination of the theory and research pertaining to the Cuisenaire rods which leads the author to accept them as a viable product capable of being extended into the set of negative integers. He then presents the design of a new product for negative numbers that is an extension of the rods and affirms the validity of the design by measuring it against the previously discussed related implications of theory. (MN)