In recent years, wearable antenna design has grossed research interest amongst academicians and researchers due to its versatile application in body area networks for transmitting/receiving signals in sufficiently large areassuch as ICU, trauma centers in hospitals for biomedical applications at ISM (2.45 GHz) frequency range. A wearable antenna is highly flexible in nature making it popular and demanding. What makes it even more suitable for biomedical applications is its simple design methodology and ease of integrationonpatient's dress/clothes for antenna placement in wireless communication. This paper presents a thorough investigation of various antennadesign methodologies to design a flexible wearable antenna that can be mounted on textile material for body-centric wireless communication. The traditional antenna design uses non-flexible substrate materials (such as FR-4, RT duriod, foam, etc..) having medium to high dielectric constant. This results in generation of surface wave losses which reduces antenna transmission capabilities. Flexible wearable antennas, on the contrary, uses ordinary textile materials used as a substrate whose dielectric constant is very low thereby providingreduced surface wave losses. As wearable antennas are mounted on textile fabrics it is possible to use these antennas to implant them on patients' bodies(inside/outside on the clothes) for transmitting the patients' body parameters (such as body temperate, heart rate, etc..) measured using various sensors/transducers. In this paper,a thorough review of different types of substrate materialsused for designing flexible wearable antennas is done.