Modal is a regenerated cellulose fibre. That means it starts as real plant material, usually beech wood pulp, which is dissolved into a solution and then pushed through a spinneret to be re-formed as fibre. It is not a natural fibre in the way cotton is, and it is not a synthetic in the way polyester is. It sits in a third category, and the industry calls it semi-synthetic.

It exists because the first generation of that family, viscose, has one serious flaw: it loses a large share of its strength when it gets wet, which is why cheap viscose garments stretch, sag and go shapeless after washing. Modal is made by a modified version of the same process that yields a fibre with high wet strength. Same raw material, better behaviour in a washing machine. It was developed in the 1950s and the Austrian producer Lenzing trademarked the name Modal in 1977.

TENCEL is the piece that confuses people. TENCEL is not a fibre. It is Lenzing's brand, and it covers two different things: TENCEL Modal and TENCEL Lyocell. Lyocell is made with a different solvent process, run as a closed loop that recovers most of the solvent, which is why it is generally the more environmentally defensible of the two. So a label reading TENCEL Modal is telling you the producer, not a separate material.

The reason modal dominates sleepwear and underwear is a combination of three properties. It is more absorbent than cotton, so it moves moisture off skin rather than sitting damp against it. It has a fluid drape, so it falls rather than holds a shape, which is what makes a modal slip skim instead of tent. And it resists pilling far better than viscose, so it stays smooth through repeated washing instead of going fuzzy at the friction points.

What it does not do is hold structure. If you want a crisp collar, a shirt that stands away from the body, or anything tailored, modal is the wrong fibre and no amount of blending fixes it. It also wrinkles more readily than a synthetic, though less dramatically than linen. And it is warm in a specific way: it insulates when still and cools when moving, so it is better for sleeping in a cool room than for a hot, humid one where a loose cotton weave will feel better.

Care is simple and worth following. Cool wash, low or no tumble dry. Heat is the thing that kills modal, and a hot dryer will shrink and harden a garment that would otherwise have lasted years.

Cotton is the honest comparison, because it is what modal replaced. Cotton is more breathable in still, humid heat, tolerates a hot wash, and gets softer with age rather than simply staying soft. Its weaknesses are that it holds moisture rather than moving it, takes a long time to dry, and creases hard. Combed or pima cotton, with longer staple fibres, is the version worth paying for; it pills less and feels smoother than a standard short-staple cotton at the same weight.

Weight matters more than fibre for how a garment behaves. A ribbed knit at a heavier gauge holds its shape and reads as clothing. A fine jersey at a low weight drapes and reads as sleepwear. Two garments in the same fibre can behave completely differently for this reason alone, which is why a fabric name on a label tells you less than people assume.

Silk is the original, and modal was engineered to imitate its drape and hand at a fraction of the price. Real silk still wins on temperature regulation and on the way it looks under light. Washable silk, which most sleepwear brands now use, is silk finished so that a cold gentle machine wash will not ruin it. It is a genuine improvement over dry-clean-only, not a marketing line, but it still wants cool water and air drying.

Is modal a natural fabric? No, and no honest label will say it is. It is made from plant cellulose but requires significant chemical processing, which puts it in the semi-synthetic category alongside viscose and lyocell.

Is modal better than cotton? For sleepwear and underwear, usually, because it moves moisture and drapes better. For a hot humid climate, or anything you want to wash hot, cotton is the better choice.

What is the difference between modal and TENCEL? TENCEL is a brand name owned by Lenzing that covers both TENCEL Modal and TENCEL Lyocell. Modal is the fibre type. A garment can be modal without being TENCEL, and TENCEL can mean lyocell rather than modal.

Does modal shrink? Very little in a cool wash, noticeably in a hot dryer. Heat is the risk, not water.

Is modal breathable? It is absorbent rather than airy. It pulls moisture away from skin efficiently, which feels cool in a temperate room, but a loose cotton weave will feel cooler in humid heat.

Is modal worth the extra money over viscose? Yes, and this is the one place the price difference is easy to justify. Viscose weakens when wet and goes shapeless; modal does not. Over a garment you wash every week, that is the whole difference.