Pugs look adorable in jackets and sweaters, but you need to still keep an eye on them. Extreme hot and cold are very dangerous to pugs, due to their unique physiology. While winter clothing helps, you still need to keep an eye on your pug in extreme weather.
Pug Body Type
Pugs have several things going against them in the temperature-resistance department. They have a rather thin coat. Their fine, short hair doesn't do a great job protecting them from cold temperatures. Additionally, they have relatively small bodies, resulting in a small surface-to-volume ratio, making it easy for them to lose heat to the environment. This predisposes them to a poor tolerance for cold.
Pugs and Extreme Temperatures
Pugs don't adapt well to extreme temperatures in either direction. You must keep an eye on your pug in very cold and very hot weather. Fortunately, pugs require very little exercise, so they don't have much reason to spend a lot of time outside when the weather is inclement. Using a jacket or a sweater can offer further protection, but the first line of protection should always be you.
Sweaters and jackets can help a pug in cold weather. They're great for giving these little dogs an extra layer of protection when temperatures are unfriendly. However, even with clothing, pugs are not Alaskan huskies by any means. You should use cold-weather clothing as extra protection, but do not leave your pug out in the cold. Observe your pet. If she begins to shiver or gets too cold, bring her inside ASAP.
Never put clothing on your pug in warm weather. Pugs overheat even more easily than they freeze. You should also pay very close attention to your pug when she is exercising. Avoid sweaters/jackets when taking your pug for exercise, unless in the coldest weather. Even then, always keep an eye on your pug. If she has a hard time, get her out of the clothes.