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Plant fibres composites (PFCs) have lately gained significant interest due to their environment friendly aspects and enhanced physical and mechanical performances. A subcategory of PFCs that uses thermoplastics has become widespread with the advent of the additive manufacturing industry. This work is focused on the investigation of the thermoformability of PFCs made using two techniques: hot-press thermoforming and 3D printing. The hot-press technique is widely used by researchers and industrials, whereas 3D printing is celebrated as a technique that can produce very complex shapes in a relatively facile manner. The main goal of the work here is to explore the ability of each technique to produce PFC objects without requiring elaborate setups. Another objective is to assess their integration, alongside the use of other assistive techniques and tools like a vacuum bagging and oven. These assessments have been aimed at achieving better manufacturing outcomes, such as a lower fabrication time. In the part related to the optimization of the hot-press technique, flax and polypropylene (flax/PP) laminates have been fabricated and examined, mechanically and aesthetically, for their sensitivity towards five fabrication parameters and two post-processing variables. The produced Flax/PP laminate has shown potential use as a replacement to its glass counterparts, due to their advantageous specific stiffness. Regarding the 3D printing technique, a fused filament fabrication (FFF) printer and Polylactic Acid (PLA) filament have been used to prototype auxetic cellular structures. The study begun by looking at the effect of the filament colour and the printer deposition angle on the mechanical performance of the prints. Afterward, auxetic cellular structures were printed and examined. Flat-shaped honeycombs Poisson's ratio (PR) and dome-shaped honeycombs indentation and drop impact properties have been investigated. Dome-shaped honeycombs, in particular, show an interesting softened post-buckling indentation, more accentuated with auxetic (i.e., negative Poisson's ratio) cellular configurations. PLA and wood-plastic composites filaments have been later successfully produced in the lab with printable characteristics using an off-the-shelf extruder. These filaments properties were found to rival their commercially available counterparts. PFCs fabrication and examination are yet to be established as a standardised industry, which is still impeded by the lack of open-access knowledge. Further developments are commented for the next big evolution in PFC laminate thermoforming technology.