Low-mass close-in exoplanets are susceptible to intense atmospheric escape. Recent studies suggested that such escaping outflow can deliver abundant aerosols to upper atmospheres and drastically inflate the observed transit radius. Here, we investigate how aerosols grow and move in escaping atmospheres and influence transit observations of exoplanets using a detailed microphysical model. We find that aerosols formed at low altitudes, such as condensation clouds, are barely transported by the outflow owing to efficient particle growth and gravitational settling, while aerosols formed at high altitudes, such as photochemical hazes, are susceptible to be entrained in escaping outflow. With sufficiently high aerosol production altitudes and rates, the outflowing aerosols can enhance the observable radius by a factor of ∼2 or even more. The outflowing aerosols produce featureless NIR transmission spectra, in agreement with the spectra observed for extremely low-density planets called super-puffs. The spectrum also shows a broad spectral slope ranging from the visible to the mid-IR as well as absorption features of the aerosols themselves, which can be tested by upcoming JWST observations. Lastly, using an interior structure model, we show that the radius inflation by outflowing aerosols is drastic only when the planets verge on total atmospheric loss. This potentially explains why super-puffs are uncommon despite the suggested prevalence of photochemical hazes on exoplanets.