How to Wash Modal Fabric

The Chemistry

Modal is frequently grouped with viscose (rayon) and bamboo fabric under the umbrella of "regenerated cellulose fibres." While that classification is technically accurate, it obscures a critical distinction in fibre architecture that makes modal behave very differently from standard viscose in the wash. All regenerated cellulose fibres share the same manufacturing foundation: cellulose from a biological source (wood pulp, bamboo, cotton linters) is dissolved using chemical processing, then extruded through small holes (spinnerets) into a setting bath to form continuous filaments. The differences between the resulting fibres come from how those filaments are produced. Standard viscose uses the xanthate process: the dissolved cellulose is extruded into a dilute acid bath where it regenerates as a solid fibre. The fibre structure produced by this process has relatively low crystalline orientation — the cellulose polymer chains are only partially aligned along the fibre axis. The consequence is that when standard viscose absorbs water, the amorphous regions between crystalline zones swell and the inter-chain forces are disrupted, causing a dramatic 40–50% drop in tensile strength when wet. Modal uses a modified viscose process with a higher draw ratio — the cellulose filaments are stretched significantly more during and after extrusion, before they fully solidify. This additional stretching forces more of the cellulose polymer chains to align parallel to the fibre axis, greatly increasing crystalline orientation. The result is a fibre with a fundamentally different internal structure from standard viscose: more of the cellulose is in ordered crystalline regions, the amorphous regions are reduced, and the fibre is less susceptible to inter-chain disruption when wet. The practical consequence is that modal has 50–80% higher wet tensile strength than standard viscose, and approximately 10% stronger when wet than when dry (slightly positive, similar to cotton, rather than strongly negative as in viscose). Modal does not need the special cold-hand-wash fragility treatment required for standard viscose or bamboo viscose. It is genuinely machine washable. Modal is produced almost exclusively from European beech trees (Fagus sylvatica). Beech wood contains cellulose with somewhat longer polymer chains than many other wood sources, which contributes to the improved fibre properties. The main commercial producer is Lenzing (Austria), which markets its modal under the brand name TENCEL Modal. This brand has also driven environmental credentials for modal — beech trees require no irrigation and grow on certified managed land. Modal also has substantially higher moisture absorbency than cotton: it absorbs approximately 50% more water by weight than cotton. This makes modal clothing feel very soft and cool against the skin because it draws moisture away from the body efficiently. It also means modal takes longer to dry than cotton fabrics of the same weight. This is worth knowing for planning drying time, not a concern for the washing process itself. Modal is colourfast under normal washing conditions — the fibre accepts reactive dyes well and the dye bonds are stable in the 40°C range typical for modal care. However, like all cellulosic fibres, modal will fade under repeated high-temperature washing or bleaching. Avoid chlorine bleach entirely, which degrades all regenerated cellulose fibres. Modal vs Tencel (Lyocell): Tencel uses a different process — the NMMO (N-methylmorpholine N-oxide) closed-loop solvent process instead of the xanthate process. Tencel preserves even longer cellulose chains and typically produces fibres with even higher wet strength than modal, plus a significantly lower environmental impact due to solvent recovery. Modal is close to Tencel in practical washing terms but slightly less strong when wet. Both are far superior to standard viscose. Modal vs cotton: Cotton is slightly stronger when wet than modal (cotton: +15–20% when wet; modal: +10% when wet). Both are machine washable in similar conditions. Modal feels much softer than equivalent cotton due to the smooth, consistent surface of the drawn fibre. Modal has better moisture absorption than cotton.