The design is printed on one side, but shows through to the other side in reverse. The majority of flags are created this way, including most state flags and corporate flags. A single/reversed flag is lightweight and is the most cost-effective flag option.
The design is printed on both sides of the flag so the design shows accurately on each side. Typically, the flag is technically two single-sided flags that have been sewn back to back, making it much thicker and heavier. An additional panel of fabric is placed in the middle so that each image doesn’t bleed through to the other side.