Laboratory-scale research had shown the potential of using cotton burr/stem (CBS) as fiber filler in thermoplastic composites. This study evaluates the potential of using waste materials from cotton harvesting/ginning operations, CBS and cotton module wraps (CMWs), as a filler and substrate in thermoplastic composites at commercial scale. The study also compares the effect of scale-up from laboratory to commercial scale on the properties of the thermoplastic composite materials. Two separate commercial trials were conducted to manufacture thermoplastic composite boards with (a) 0, 12.5, 25 and 37.5% by weight of CBS and (b) up to 30% by weight of CMW. Testing of these samples showed that commercial-scale samples with 12.5% CBS had all properties comparable to those made with wood filler. At higher substitution rates, CBS tended to increase water absorption and coefficient of thermal expansion, and increase nail-holding capacity (NHC) and hardness in commercial-scale samples. This study also showed that CMW can be substituted by up to 30% by weight without deterioration of properties in comparison with a commercially available product. Scaling of the process had significant influence on all properties tested, expect NHC. In general, all commercial-scale samples exhibited physicomechanical properties within the range of properties reported for commercially available wood–plastic composite decking materials.