Flexible antennas are robust, lightweight and can withstand mechanical strains up to a certain extent. In order to make the antenna flexible, alternative materials to replace existing substrates that are rigid have been considered. The basic idea is to lay a thin metal strip on top of a flexible substrate. This metal must maintain their conductivity even when it is stretched [1]. Several flexible substrates have been reported such as polymer, micro fluids/liquid metals, paper, plastic, etc. Polymer-based antennas become a popular topic in the field of flexible antennas. According to [2-4], different approaches using polymers as flexible substrates have been identified - this included liquid crystal polymer, polydimethylsiloxane employing silicone elastomers or ceramic composites, and high conductivity polymer like carbon nanotube. The advantages of using polymers as the flexible substrate is they are inexpensive, able to withstand mechanical strains, can be mixed and cured at room temperature and their dielectric properties can be varied. However, the preparation process is tedious. Other researchers have successfully designed flexible antennas on micro fluids or liquid metals [5-6]. The liquid metals are filled into micro-fluid channels. These metals help prevent loss of electrical conductivity when the antenna is deformed, and it can conform to any shape without strain. However, it is a difficult process to shape the liquid metal into the channels. This is because the tendency of the metal to fill unevenly or create pockets of air bubbles. Hence, this method only applies for channels with a cross section that has a bigger aspect ratio. Paper as a flexible substrate has also gained a lot of interest due to its low cost, ease of fabrication and organic based structure. However, flexible antennas fabricated on paper substrate are not quite suitable for outdoor applications [7-8]. On the other hand, plastic or polyethylene terephthalate (PET) substrates have also been identified as possible candidates. PET is cheap; hence it is useful for cost effectiveness. However, the losses of this substrate partially affect the antenna performance [9-10]. In this paper, rubber, which is a natural polymer, is chosen as the flexible substrate. The mechanical properties of rubber make it a good candidate for this purpose. According to [11-14], rubber can naturally and forcibly retract to its original dimensions after deformation. Besides, rubber can be processed into a variety of shapes and can be attached to metal inserts or mounting plates. This paper will explore the viability of using rubber as a substrate of microstrip antenna by carrying out some preliminary studies on the effect of substrate and metal thickness, and relative permittivity on antenna performance.