Microstructural changes induced by helium implantation in materials lead to volumetric swelling and mechanical property changes. How these properties are linked and establishing direct relationships can be difficult due to the underlying material’s microstructure evolution. Some materials also experience a phase change due to irradiation damage making them even more complex to analyze. Here, single crystalline Si (100) was used to establish a relationship among these parameters. The swelling height as a function of implantation fluence can equally fit a linear relationship. Solely irradiation induced defects are observed at low fluence below 5.0 × 1016 ions/cm2. An abrupt amorphous and crystalline mixed layer of ∼200 nm thick within a highly damaged polycrystalline matrix is observed when implantation fluence exceeds 5.0 × 1016 ions/cm2, leading to the appearance of irradiation induced swelling and hardening behavior. As the fluence increases beyond 1.0 × 1017 ions/cm2, the amorphous layer expands in size and the bubble size distribution takes the form of a Gaussian distribution with a maximum size of up to 6.4 nm, which causes a further increase in the height of swelling. Furthermore, irradiation induced softening appeared due to the enlarged bubble size and amorphization.