Sweatshirts used are 50% Polyester / 50% Cotton by Gildan or similar brands, depending on availability or color and sizes.
Multi-color graphics (greater than 3 colors) and photographic designs are produced using Direct To Garment technology. This process creates a graphic that feels very smooth and soft, softer than silk screen. The graphic is relatively vibrant, but the colors are not as vibrant as silkscreen since silkscreen inks are much thicker than DTG printer inks. You can expect a shirt that lasts a very long time.
1 to 3 color graphics typically use heat transfer materials that are very durable and feel similar to silkscreen inks.