What kind of finish is the 'back side brushed processing' mentioned in the description?

It is a finish made so that the outside and inside look different. The outer surface retains the unique texture of single jersey as is, and brushed processing is added only to the back side, which corresponds to the reverse side^[1].

Looking at the two terms separately makes it easier to understand. Single jersey refers to a knitted fabric knitted in a single layer; it is thinner and lighter than double-knit fabrics, and its characteristic is that the outer and back surfaces turn out differently. Brushed processing is a process in which the surface of that fabric is scratched with a roller studded with needles or wire points to raise the ends of the fibers, which is commonly called fleece or napped finish. When an air layer forms between the raised fine nap like this, the touch against the skin becomes softer and less body heat escapes.

The part to pay attention to during care is also this nap side. Because repeated friction tends to flatten or clump the napped surface into pills, it is generally safer to turn it inside out, place it in a laundry net, wash it on a gentle cycle, and avoid the strong heat of a dryer. However, how the washing instructions for this top are actually guided is a separate matter, so it is better to prioritize the care label attached to the product.

hmmm, this reads as a finish chosen to alter only the surface that touches the body, rather than making the fabric thicker.