How do I stop a white T-shirt from looking see-through?

Short answer: White fabric looks transparent mainly because light passes through gaps between yarns and through thin yarns, and because there is no dye to absorb light. The main fixes are a denser fabric and the right yarn: a higher finished GSM, a tighter knit with more stitches per centimetre, a finer combed or compact yarn that fills the structure more evenly, or a different structure such as interlock or double knit. Optical brighteners and full bleaching can make white look brighter but do not fix see-through fabric. Some brands use a slightly heavier fabric only for white, or add a lining or double layer at the front. Compare candidates by holding swatches over a dark printed card under daylight and by a simple light-box check, then confirm on fitted samples.

Why white looks see-through

• No dye to absorb light, so gaps and thin areas show.
• Loose knit or low GSM.
• Uneven or hairy yarn creating thin spots.
• Stretching across the body opens the structure further.

How to improve opacity

• Increase finished GSM, for example from 160 to 200 or more.
• Tighter stitch length or higher machine gauge.
• Compact or combed yarns.
• Interlock, double knit or heavier rib structures.
• A double layer at the chest for fitted styles.

How to compare

• Lay swatches over a black-and-white printed card and photograph in daylight.
• Check stretched fabric, since opacity drops when worn.
• Compare GSM and dimensional change with ISO 5077 so the heavier fabric still meets fit.

A worked example

The brand tests its 165 GSM white against a 200 GSM tighter jersey and a 190 GSM interlock. The 200 GSM jersey covers the card text well and keeps the same hand; the interlock is the most opaque but feels warmer. The brand switches white to the 200 GSM jersey, keeping colours on the original fabric.

Communicating with customers

If white stays slightly translucent by design, as with lightweight summer tees, say so on the product page and show the shirt worn in daylight. Clear photos and a fabric weight in the description reduce disappointment and returns more than a vague promise of being opaque.

Limits

No knit cotton tee is fully opaque in every light. Body shape, fit and the wearer's skin and underwear colour all change perception.

Facts, recommendations and uncertainty

Established: opacity comes mainly from fabric density and yarn evenness, not from brighteners. Recommendation: use a denser fabric or structure for white and compare stretched swatches. Uncertain: how opaque your customers expect a white tee to be.

Sources and further reading

• ISO 3801:1977 — Mass per unit length and mass per unit area (woven fabrics)
• ISO 5077:2007 — Determination of dimensional change in washing and drying

Standards and regulations are referenced by their published scope. Test parameters, cycles and pass levels should be agreed with your laboratory for the specific product; legal requirements should be confirmed for each destination market.