You've probably heard that whisky connoisseurs don't just talk about tasting, but also about nosing. In this case, they don't use a tumbler, but rather a so-called nosing glass.
The nosing glass is similar to a sherry glass. The bulbous shape ensures that the aromas spread well, but cannot escape immediately due to the narrow opening. This allows experienced noses to quickly "sniff out" and name the individual aromas in the whisky. These glasses also have a curved rim so that the contents can flow broadly and evenly into the mouth. Since color plays a major role alongside the smell, nosing glasses are also best made of crystal glass.
If you compare the nosing glass with a tumbler, you will quickly see that it has a much thinner glass. This makes it easier for connoisseurs to warm the whisky slightly with their hands. Single malts should always be drunk at room temperature and without ice.