The most characteristic feature of a Side Support Bra is the sectioning of the cups, which is done to properly place breast tissue to appear rounder and fuller. The more the sections, the better the support. Most also have supportive cup extensions that run around under the arm- which is where the name, side support, originates.
This bra style is the only one that offers additional support from the sides of the bra. The large panells on the side of the bra mainly prevent the breasts from spilling sideways and creating that “east and west” breast appearance. With a side support bra, your breasts are pushed inward, meaning you won't stick out from the side and the front will appear more narrow.
Most side support bras contain a broader bra strap, meaning that those with a heavier bust have a better hold and lift in comparison to bras with thinner straps.
Side support bras are also typically made of fabrics that do a great job at cooling and wicking away sweat. This is why lots of Sports Bras fall into the category of side support.