The use of low-cost renewable natural fibres as reinforcements for structural composites is attractive but requires specific considerations over that of textile industry requirements. Textile yarns are twisted for processability and increased tensile strength. However, reinforcements employing twisted yarns produce poorer composites due to hindered yarn impregnation, inadequate wettability and compromised orientation efficiency. Whilst assessing the physical properties of select plant fibre yarns that determine reinforcement/composite properties, a strong correlation between yarn twist and compaction is observed. This manuscript also examines a novel plant fibre treatment method using hydroxyethylcellulose (HEC). HEC treatment not only enables intra- and inter-yarn binding thus allowing easy preparation of aligned fabrics, but also improves yarn mechanical properties whilst maintaining physical properties such as low twist. It is noticed that low twist yarns are more responsive to HEC treatment; the tenacity and stiffness of low twist flax is observed to increase by 230 and 75%, respectively.