"GSM" and what it means for buying blank t-shirts etc
GSM stands for "grams per square metre" and is a guide to fabric weight. It is not necessarily a guide to fabric quality or even warmth. There are other factors to consider, such as the fibre and its origins, the way it was spun or manufactured, and the weave. Some high-tech cotton fabrics produce durable, opaque t-shirts with relatively low GSM and a superior feel to thicker fabric densities. With fleece hoodies, however, as a general rule only, the heavier the GSM, the warmer to wear, although once again fabric composition and weave must be taken into account.
What makes slim-fit t-shirts different to regular t-shirts?
Slim fits are cut more to the body shape, with a narrower and slightly higher sleeve line. You don't have to be "slim" to wear slim fit t-shirts - it's all about what fit you prefer in any size. Most slim fit t-shirt styles range in sizes up to ladies 18-20 and men's 2XL-3XL, so there's a slim-fit to fit almost everyone.