Pectoral implants are made of a flexible silicone that is placed through the underarm in between the two chest muscles. Pectoral implants will give a man the appearance of highly developed chest muscles.This procedure can be done either as a cosmetic procedure or a procedure due to a birth defect.ectoral implants are made of a flexible silicone that is placed through the underarm in between the two chest muscles. Pectoral implants will give a man the appearance of highly developed chest muscles.