**5. Conclusions**

In this study, the amaranth stem was used to develop innovative building materials. Representing up to 80% ( *w*/*w*) of the plant aerial part, the stem is made of a pith in its middle and a bark on its periphery. Firstly, a fractionation process of the stem into these two different fractions was proposed. Secondly, bio-sourced composite materials were manufactured, i.e., thermal insulating materials made from pith (in bulk or in the form of low-density cohesive blocks), and hardboards from bark. All these materials are viable alternatives to some of the commercial materials nowadays used in buildings.

For future work, the scaling-up of the fractionation process of the amaranth stems into pith and bark fractions will be an important step for its subsequent use at an industrial scale. It should allow a better profitability of this crucial step for the process. Additional developments will also have to be conducted to improve the global performance of the amaranth-based buildings materials. In particular, various post-treatments (e.g., coating, cooking, etc.) should reduce their water sensitivity on the one hand and improve their resistance to microbial growth on the other hand. The evaluation of their fire resistance and, if necessary, the addition of fireproofing products should also be considered before they are used inside houses. Lastly, as it is expected that the low-density insulation blocks from pith will be promising water regulators, their water vapour permeability will also have to be determined. All these developments will undoubtedly facilitate the subsequent introduction of these different bio-sourced building materials on the market.

**Author Contributions:** Conceptualization, P.E.; methodology, P.E. and L.L.; validation, P.E., O.M., and T.T.; formal analysis, P.E. and O.M.; investigation, G.d.L. and L.L.; resources, S.B. and T.V.; writing—original draft preparation, P.E. and G.d.L.; writing—review and editing, P.E. and O.M.; supervision, P.E.; project administration, P.E. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not Applicable.

**Informed Consent Statement:** Not Applicable.

**Data Availability Statement:** Data sharing is not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
