Due to their light‐weight and cost‐effectiveness, cellular thermoplastic foams are considered as important engineering materials. On the other hand, additive manufacturing or 3D printing is one of the emerging and fastest growing manufacturing technologies due to its advantages such as design freedom and tool‐less production. Nowadays, 3D printing of polymer compounds is mostly limited to manufacturing of solid parts. In this context, a merged foaming and printing technology can introduce a great alternative for the currently used foam manufacturing technologies such as foam injection molding. This perspective review article tackles the attempts taken toward initiating this novel technology to simultaneously foam and print thermoplastics. After explaining the basics of polymer foaming and additive manufacturing, this article classifies different attempts that have been made toward generating foamed printed structures while highlighting their challenges. These attempts are clustered into 1) architected porous structures, 2) syntactic foaming, 3) post‐foaming of printed parts, and eventually 4) printing of blowing agents saturated filaments. Among these, the latest approach is the most practical route although it has not been thoroughly studied yet. A filament free approach that can be introduced as a potential strategy to unlock the difficulties to produce printed foam structures is also proposed.

Cellulose is an abundant and sustainable material that is receiving more and more attention in different industries. In the context of additive manufacturing, it would be even more valuable. However, there are some challenges to overcome in processing cellulose-based materials. Therefore, this study used a new thermoplastic cellulose-based granulate to show its potential in filament extrusion and the fused filament fabrication printing process. Furthermore, the mechanical properties were investigated. It was shown that filaments with a suitable and uniform diameter could be produced. A parameter study for printing revealed that adhesion of the material on the bed and between layers was an issue but could be overcome with a suitable set of parameters. Tensile bars with different orientations of 0°, +/−45°, and 90° were printed and compared with injection-molded samples. It could be shown that different mechanisms (single strand breakage, shear failure) caused fracture for different printing orientations. In comparison with injection-molding, the printed parts showed lower mechanical properties (moduli of 74–95%, a tensile strength of 47–69%, and an elongation at break of 29–60%), but an improvement could be seen compared with earlier reported direct granule printing. The study showed that FFF is a suitable process for the new cellulose-based material to fabricate samples with good mechanical properties.

Combining multiple filaments in material extrusion (MEX) to tailor mechanical properties is increasingly significant in science and applications. However, understanding the interaction between different materials, the influence on the mechanical properties and the predictability of such properties is still poor. Therefore, this study investigates the tensile and flexural behavior of 3D‐printed sandwich‐type composites made of polypropylene (PP) and glass fiber‐filled polypropylene (PPGF). The materials exhibit different mechanical properties, with PP being more ductile and flexible and PPGF being more brittle and stiff. Various contents of PP and PPGF were used. Measured mechanical values were correlated with theoretical predictions. The tensile properties scaled linearly with the material composition, covering a range of moduli and strength values between 500–2910 MPa and 18–43 MPa, respectively. A rule of mixture could be applied, although PPGF layers tended to crack early. The ductile nature of PP allowed for bridging cracks, preventing premature failure. In flexural tests, the shell material dominated modulus, strength and failure mode. The samples with PPGF shells failed by cracking, while specimens with PP shells showed high deformation without clear failure. By varying contents and layer order, flexural moduli ranging from 680 to 3180 MPa and flexural strengths from 25 to 65 MPa were reached. Additionally, the study demonstrated that theoretical calculations and predictions of tensile and flexural moduli were highly accurate with an average deviation of 6.0% and 1.4%, respectively. This highlights the potential for tailoring mechanical properties based on the characteristics of PP and PPGF.Highlights: High PP/PPGF interface adhesion ensures reproducible multi‐material printing. Whole range of mechanical properties from ductile PP to stiff PPGF is reached. Order and amount of both materials determine failure behavior. Analytical prediction of modulus is very accurate.

Polypropylene (PP) has been used very little as additive manufacturing material so far. Commercial filaments often consist of copolymers or blends and thus do n