The most important factor is the fiber(s) from which the fabric is made. Some fibers are strong and make a strong yarn and fabric while others are weak and give a weak fabric. Next in importance is the type of yarn made from the fiber. Is it thin or thick, tightly or loosely twisted? A tightly twisted yarn, for example, maybe stronger than a loosely twisted one. Lastly, the way the fabric is made must be examined. Which type of weaving or knitting has been used? A thick fluffy cloth will be warmer than a thin smooth fabric made of the same fiber.
One function of clothes is to help to keep the temperature of the body at about 37°C (98.4°F). Therefore in cold weather the heat produced by the body must not be allowed to escape, but in warmth weather and during exercise the body needs to lose heat to prevent the body temperature rising. For cold weather it is sensible to choose a fabric which retains heat which does not 'conduct' heat away from the body. It's an insulator, and any fabric which traps a lot of air between the threads and against your skin will be warm, as well as being light. The amount of air in a fabric is the most important factor in determining its warmth. In addition some fibers themselves are good conductors of heat. A good example of these is linen. Others fibers like wool and silk are poor conductors of heat. Wool is also a crimped or wavy fiber, so that air is always trapped in woolen yarns and fabrics and makes them warm. This is particularly important, when you are buying a coat, taking into consideration the unexpected change in weather.
For clothes to stay smart they must not crease easily and become baggy and shapeless. This is particularly important for clothes which are worn everyday. However it matters less for clothes which are only worn for a few hours. Fabrics which do not crease easily also called resilient - one of the best examples is silk, which if crumpled into a tight ball in the palm of your hand will spring out uncreased when released.
It is common knowledge that some fabrics get dirty faster than others. Clothes with smooth finishes stay clean longest. Hairy, rough or fluffy surfaces pick up the dirt which is caught on the minute hairs of the fibers. Linen fibres are long and smooth, making smooth threads and smooth fabrics which remain clean longer. Wool fibres have rough scales on them, so that the fabrics always get dirty faster than linen ones under similar conditions.
Another factor that should be considered in choosing clothing is safety. Many children and adults are injured and some killed each year from burning clothing. Children's clothes, particularly nightwear and party clothes, should be made from material which does not catch fire or which will only do so with difficulty and will not flare up. In this category of materials are wool, silk thin nylon fabrics with 'safe from fire' labels and flame-proofed cotton.