Purpose: This paper reports some results from a comparative study of the behavior of fresh and exposed samples of an EPDM-type water-swelling elastomer. Design/methodology/approach: Experiments were designed and performed in line with standard ASTM test methods and in consultation with petroleum development engineers. Small test fixtures were designed and fabricated, to be used together with standard testing equipment. Elastomer response was studied for hardness, compression set and tensile set (at different temperatures and for different periods of time), tensile properties (fracture strength and percent elongation), and swelling (gradual thickness and volume change with exposure to saline solution). In the swelling test, unconfined samples and samples mounted on steel plate were tested for a total duration of 1000 hours (roughly 45 days) in salt solutions of different concentrations and at different temperatures. Findings: Exposed elastomer samples (EPDM1) showed higher hardness than fresh samples (EPDM2). Compression set values of exposed samples was significantly higher than fresh ones. Tensile set values were almost the same for the two sample types after 10-min test, but were higher fort exposed elastomer after longer-duration tests. Stress-strain graphs for both sample sets were almost linear, in contrast to highly nonlinear graphs for usual rubber-type materials. Values of fracture stress and elastic modulus for exposed elastomer were noticeably higher, but percent elongation was lower. Swelling behavior showed a fluctuating trend with increasing swelling time for both elastomers. For same temperature and salinity, fresh elastomer samples yielded much more swelling than exposed samples. All of these observations indicate that such swelling elastomers lose flexibility and swelling capacity when exposed to sun and moisture, etc for extended periods of time. Practical implications: Results of this study can be used by oilfield engineers to gauge the suitability of these elastomers for downhole applications. Material properties after swelling can be used by designers using FEM or other numerical simulation methods for improvement of elastomer-based sealing and packer design. Comparison of fresh and exposed elastomer samples highlights the significant change in material response due to exposure. Originality/value: The paper presents a comparison between material properties of fresh and exposed samples of the same water-swelling elastomer. Such a comparative study, highlighting the effect of exposure on material response of an elastomer, has not been carried out before.