A white T-shirt can look solid under fitting-room lights, then show skin or an underlayer when you step outside. That surprise is not explained by cotton content or fabric weight alone. Coverage depends on how the knit blocks light, the shade, how much the fabric stretches on your body and what sits underneath. This guide focuses on judging sheerness before you buy—or deciding what to wear under a tee you already own. For the separate question of how fabric mass affects warmth and drape, see our T-shirt GSM guide.
Why can a white T-shirt look see-through?
Sheerness is a visual result: light passes through a fabric and the contrast behind it remains visible. A white or pale surface tends to disguise that contrast less than a deep colour, but shade is only one part of the answer. A dark T-shirt can still be lightweight, and a white one can have good coverage; colour does not tell you how tightly the yarns are packed.
Most T-shirts use knitted fabric. The loop pattern, yarn size and spacing affect how much of the background can be seen through the cloth. A label that says “100% cotton” identifies the fibre, not the knit density, finishing or coverage. Two cotton jerseys can behave differently even if their fibre labels look the same.
Fit and lighting change what you see as well. When a tee pulls taut across the chest, shoulders or stomach, the knit can open up and reveal more underneath. A garment that looks opaque lying flat or hanging on a rack may look different when it is stretched over the body. Strong daylight or backlighting can also expose sheerness that warm shop lighting hides.
So the useful question is not simply “Is this cotton?” or “Is it heavyweight?” It is “How does this particular fabric look in the light and fit I will actually wear it in?”
Does GSM tell you whether a white tee is opaque?
GSM means grams per square metre: the mass of a set area of fabric. It is a helpful comparison point, but it is not an opacity rating or a guarantee of quality. Knit structure, yarn, fibre, finishing, colour and fit all affect how much light and contrast show through. A higher GSM can mean more fabric mass, but two fabrics at a similar GSM can still look and behave differently. There is no universal GSM number that guarantees every white T-shirt will be non-see-through.
For broader context on fabric composition and construction, see AGR5V’s streetwear fabric guide. The main point here is narrower: use GSM as one clue, not a substitute for checking coverage. AATCC has a separate laboratory method for measuring textile light-blocking with a photometer; a fabric-weight number on a product page is not the same thing as a reported light-blocking result.
For example, AGR5V’s current product pages list these white options and specifications:
- Everyday Cotton Tee: 100% cotton, 180 g/m², regular fit; the listed colours include Lucent White.
- The Boxy Tee: 95% cotton and 5% spandex, 210 g/m², boxy drop-shoulder fit; White is listed as a colour option.
- The Foundation Heavy Tee: 100% pure cotton, 260 g/m², loose relaxed fit; listed colours include White, White Gray and Apricot.
Those are the details the store publishes—not results from an opacity test. The product pages do not state that any of these tees is see-through-free, so the specs should not be read as a promise of coverage. Colour and size options, and stock for individual variants, can change; check the selection on the product page before ordering.
How to check a white T-shirt before you buy
If you can see the garment in person
- Use a single layer. Hold the fabric towards a bright window or other daylight and place your hand or a plain contrasting object behind it. Notice whether outlines show. Do not fold the fabric over itself for this check: two layers can hide what one layer reveals.
- Check it on your body. Try it with the kind of underlayer you would normally wear. Look at the chest, shoulders, stomach and back, then raise your arms, sit and move. The fabric may stretch or pull differently once you move.
- Change the light. Look near a window or outside if practical, not only beneath warm shop lights. If the tee is for an outdoor outfit, assess it in daylight rather than relying on a fitting-room mirror.
- Notice the fit as well as the cloth. If the fabric is pulled tight, try a cut or size that skims rather than strains. Compare garment measurements with a tee you already like; AGR5V’s T-shirt fit guide explains what to check beyond the size label.
A hand-under-fabric check is a quick screen, not a formal pass-or-fail test. Opacity is judged under particular lighting and against a particular background; what matters most for wearing the tee is how it looks on you, in the conditions you expect.
If you are shopping online
- Read the full specification. Look for fibre percentages, stated GSM, fit and any description of the knit or construction. “100% cotton”, “premium” and “heavyweight” are not opacity test results.
- Look for useful photos. On-body images and close-ups can help, especially if the fabric is shown in bright or natural light. A white tee photographed against a white studio background may make coverage difficult to judge.
- Search customer reviews carefully. Terms such as “see-through”, “sheer” or “transparent” may surface relevant experiences. Treat reviews as individual reports: lighting, fit, underlayers and personal expectations vary.
- Check sizing and the returns policy. Use the garment measurements to avoid a fit that pulls across the body. If transparency is a deal-breaker and the page gives no useful detail, ask the retailer before buying and check whether the item can be returned after trying on.
None of these checks can certify a garment from a product photo alone. They help you make a better-informed choice and avoid treating a fabric-weight number or a fibre label as a promise.
What to wear under a white tee that shows through
If you like the shirt but want less contrast underneath, try a smooth underlayer close to your own skin tone. “Nude” is not one universal colour; the aim is to reduce the difference between the underlayer and your skin beneath the white fabric. A bright white layer can still show as a distinct edge, while a dark or patterned one may stand out more. Test the combination with the actual tee if you can.
Choose an underlayer that suits your comfort and the neckline or sleeve of the T-shirt. A smooth singlet, camisole or bra can work, depending on what you prefer; avoid a layer that is so tight it creates new lines or pulls the outer tee. If you want the underlayer to be visible, make that an intentional styling choice rather than expecting it to disappear.
An open overshirt or light jacket can provide another layer, but it may not be comfortable in hot or humid weather. In Queensland heat, it can be easier to choose a tee whose coverage you have checked in daylight than to rely on an extra layer. If you do not specifically need white, a darker shade can disguise contrast more readily, though it still does not prove the fabric is opaque. AGR5V’s Cotton Tee — Dark Colour Series is one current darker-colour option; its product page lists 100% cotton at 180 g/m², not an opacity rating.
What if a T-shirt became sheer after washing?
First compare it with how it looked when new. Check for visibly thin or damaged areas, stretching, and whether the shirt now fits more tightly across the body. A change in appearance can have more than one explanation, so avoid assuming that a softener, starch or a hotter wash will restore coverage. Follow the garment’s care label and inspect the fabric in daylight after it is dry.
If the main change is that the tee has shrunk, twisted or lost its original fit, AGR5V’s T-shirt shape-loss guide covers possible reasons a tee changes over time. That is a separate issue from an opacity test: care may help preserve a garment’s condition, but it cannot turn an untested fabric specification into a guarantee of coverage.
Choosing a cut and colour without guessing
Choose a fit for the silhouette you want, then check that it does not pull where coverage matters to you. A regular tee may skim the body; a boxy or oversized cut offers more room, but neither shape guarantees opacity. If you want to compare relaxed cuts, browse AGR5V’s oversized T-shirt collection. For staple tees and other basics, The Core Collection is another live range to compare. Use the individual product pages for the exact fibre, weight, fit, colour and current variant availability.
You do not need to buy a heavier tee—or buy from any particular brand—to solve a see-through problem. The most reliable approach is to check a single layer in strong light, assess the fit on-body and choose an underlayer or colour that gives you the coverage you want.
Frequently asked questions
Why is my white T-shirt see-through even though it is 100% cotton?
“100% cotton” describes the fibre, not how densely the fabric is knitted or how it will look when stretched. Yarn and knit construction, the fit, the light and the contrast of what is underneath can all affect the appearance.
What GSM is not see-through?
There is no single GSM that guarantees every white tee will be opaque. GSM measures mass per square metre; it does not directly measure light transmission. Treat it as one comparison point and check the fabric in daylight and on-body where possible.
Does a heavier white T-shirt guarantee full coverage?
No. More fabric mass may help in some constructions, but weight alone cannot confirm how a specific white knit will look under bright light or when stretched. Look for a stated opacity test if one is available; otherwise, use the practical checks above.
Is a white bra best under a white T-shirt?
Not always. A smooth underlayer close to your own skin tone may create less contrast than bright white, but the result depends on your skin tone, the garment and the light. Test the combination rather than assuming one colour works for everyone.
Will sizing up make a white tee less see-through?
If the current size is pulling tightly, a different size or cut may reduce tension. That can improve how the fabric sits, but sizing up does not change the knit itself and may not solve sheerness. Compare garment measurements and choose the intended fit, rather than relying on the size label alone.
How can I check a white T-shirt when shopping online?
Review the fibre and weight details, fit notes, on-body photos, customer comments and returns terms. Ask the retailer if the page does not answer your question. These steps reduce uncertainty, but only an actual on-body check in suitable light can show how the tee looks in your circumstances.
The short answer
A white tee’s sheerness is shaped by the knit, shade, fit, lighting and underlayer—not just cotton content or GSM. Treat product specifications as clues, not guarantees. Check one layer in daylight, see how it behaves on your body, and choose the coverage or layering that feels right for you.