What fabric weight and GSM mean
Short answer: Fabric weight is measured in grams per square metre, shortened to GSM. The number tells you how much fabric there is, and so something about how thick, warm and opaque a garment is, but not everything about quality.
What the number means
GSM stands for grams per square metre. A higher number means more material in the same area, making the fabric thicker, heavier and more opaque. A lower number means a lighter, thinner fabric. The figure tells you the amount of fabric, not how it is knitted.
Light weights
Light fabrics are used for summer clothing and for layers worn under other clothes. They are cooler, drape softly and dry quickly after washing. On the other hand, they are more see-through, especially in light colours, and can feel less substantial worn alone.
Heavy weights
Heavier fabrics are used for sweatwear and for tops worn on their own that should give some warmth. They cover better, hang more calmly and feel fuller. They also take longer to dry. See examples of heavier qualities in sweatwear.
Transparency
If a light coloured t-shirt is see-through, it is almost always the fabric weight and not the fibre. A light white or beige t-shirt shows more than a dark one of the same weight. Choose a heavier quality or darker colour if that matters. See bamboo t-shirt for women.
Weight is not quality
A heavy fabric is not automatically better. A light quality with a good, tight knit and good yarn can outlast a heavy quality with a loose knit. The weight tells you how much fabric there is, while yarn and knit tell you how it behaves over time.
The season
In summer, light qualities are often the most comfortable, because they let heat escape. In winter, heavier qualities give more warmth and work well alone. Many people wear a light t-shirt as the inner layer and a heavier top over it, so they can remove a layer when needed.
Fit
Fabric weight also affects how clothes sit. A light fabric follows the body more closely and drapes softly, while a heavier fabric stands away more and hides more. That is why a light t-shirt can feel closer fitting than a heavier one in the same size, even with equal measurements.
For bedding
For bedding, weight is rarely stated. Here the weave says most about how the fabric feels. Percale is light and cool, sateen is smooth and heavier, and jersey is soft and stretchy. Read more about the difference in percale, jersey and sateen.
Where to find the number
Fabric weight is not always on the garment, but it is often in the product description. If it is not, you can compare by feeling the fabric and holding it up to the light. A fabric that lets a lot of light through is usually a light quality.
Read more
If you want to know more about the fabric used for most t-shirts and a lot of underwear, and how it feels and behaves in the wash, read bamboo jersey. The knit is explained in more detail there.
Frequently asked questions
Is a higher GSM always better
No, it simply means more fabric per square metre. For summer clothing and inner layers a light quality is often better, while a heavier one suits sweatwear and tops worn alone.
Why is my white t-shirt see-through
It is usually down to a light fabric weight combined with a light colour. Choose a heavier quality or a darker colour if you want a t-shirt that covers more.
Do heavy fabrics dry more slowly
Yes, the more fabric there is, the more water it holds after washing. Heavier qualities like sweatwear therefore take longer to dry on a rack than light t-shirts.
You can find the full range at Bamboo-Clothing.com.
