From treatment to color: what to know about hemp fabric finishing

Turning raw hemp into soft, vibrant textiles requires careful finishing. Once reliant on harsh chemicals, today the process is shifting toward eco-friendly methods such as enzymatic treatments, sustainable dyeing, and mechanical softening. This article, written as part of the Hemp4Circularity project, explores what to know today about making hemp fabrics ready to wea​r.

Hemp fibres, after field retting, have a colour similar to flax. Before dyeing, the fibres, yarns, or fabrics undergo pre-treatments such as demineralisation, scouring, or bleaching. While these steps were once carried out with harmful chemicals, more sustainable methods are now available. A growing approach in the textile industry is the use of enzymes. To achieve a bright white fabric, hemp is typically bleached multiple times with hydrogen peroxide, supported by auxiliaries like wetting, dispersing, and sequestering agents.

As a hydrophilic material, hemp can be dyed using several techniques, similar to those applied to cotton or flax. One widely used process is the cold pad batch method (see figure 1). In this technique, the fabric is impregnated with dye using a foulard, rotated for several hours, and then rinsed to remove unfixed colour. The dye bath typically contains reactive dyes, alkalis (NaOH, Na₂CO₃), sodium silicate, urea, and auxiliaries such as wetting and levelling agents.

Figure 1 - Schematic representation Cold Pad Batch dyeing method

Hemp fabrics can also be printed with dyes or pigments. After dyeing or printing, an additional fixation step can be applied to improve colour fastness. 

Since hemp yarns and fabrics are generally less soft than cotton or Tencel, they often undergo a softening treatment after dyeing. Chemical softeners may be based on enzymes, condensed fatty acids, polyethylene, or silicones. Softening can also be achieved mechanically, for example with an air-flow tumbler (see figure 2). In this process, air currents—with or without steam—propel the fabric against a steel grid at very high speeds (up to 2800 m/min), resulting in permanent softness and drape.

Figure 2 - Airco 24 ©Biancalani

If hemp and flax are treated in the same way (bleaching, dyeing and finishing), the colour depth of flax is deeper compared to hemp (see figure 3). For the differences in colour fastness, see table 1.

Figure 3 - Hemp and Flax fabric, dyed with reactive dye, CPB

If you are looking for a textile finisher for bleaching, dyeing, or processing hemp yarns and fabrics, visit the online directory of companies on our Hemp4Circularity blog. For expert advice on hemp textiles, you can also reach out to the FTI Lab+ Research Centre at HOGENT.