The jeoksam (적삼) is an under layer worn by both men and women, and is fairly simple in construction. There is a wide variety of methods for constructing the collar, underarm gusset, and sleeve available. I based the proportions for my jeoksam on the pictured example, but with a wider collar and without the pleats in the crossover panel in the front. The underarm gussets are squares cut in one piece with the sleeve and folded in half, a common construction in 16th century examples.
Possible materials that could have been used in period are silk, cotton, hemp, or ramie. I opted for cotton for my first attempt. The collar is doubled, but otherwise the garment is a single layer. The construction is mostly by machine, with French seams where it was easy to do so. Hems and final collar attachment were done by hand.
Seong Myeong Su Daegam provided a large amount of research and translation help with this outfit.