Increasing the future impacts and implementation of 3D printing technologies is expected to depend heavily on the ability to develop high-performance input materials. Typical feedstocks, such as thermoplastics, are used primarily for their mechanical and structural properties and possess little intrinsic functionality to participate in desirable chemical interactions post-printing. Here, we will discuss our efforts to produce new composites for use in standard benchtop printers aimed at expanding the utility of 3D-printed components. We will detail fluoropolymer-carbon nanotube conductive composites that may be printed into flexible, low-cost, chemiresistors. Further, we will provide approaches to uniformly introduce metal-organic framework (MOF) particles into thermoplastic objects and yield composites with potential for applied use as catalysts or in separations. These MOF-composites possess unique porous features and high-surface areas and retain their sophisticated reactivity profiles (i.e. interact with and/or accommodate small molecule and gaseous guests). The formulation strategy also mitigates the poor mechanical properties typical of a pure MOF (powder). Lastly, filaments doped with lanthanide (Ln)-based nanomaterials will be described. The robust optical signatures are retained in the printed Ln-objects and used as inputs in support of a new anti-counterfeiting protocol. Characterization of feedstocks and prints by techniques such as helium ion microscopy, fluorescence, thermal analysis, and gas adsorption will be emphasized throughout the presentation.