Introduction: The porosity of the fibrous capsule around a glaucoma drainage device (GDD) may be the most important functional attribute. The factors that determine capsular porosity are not well understood. Failed GDD surgeries are usually associated with thick impervious capsules and components of aqueous have been implicated in this process. Purpose: In this study, we interrogated the effect of passage of nonaqueous fluid on capsular porosity in mature (but aqueous naïve) blebs in a previously reported GDD model (the "Center for Eye Research Australia Implant"). Materials and methods: The study was performed at two centers using 17 New Zealand White (NZW) rabbits. An experimental GDD was implanted into the subconjunctival space but without connection to the anterior chamber. After 28 days, balanced salt solution (BSS) was passed through the implant for 30 to 40 minutes at 12 mm Hg. Capsular porosity was measured as flow (μL/min) at a constant pressure. Porosity of the capsule was retested at 3 and 6 days. Results: There was a marked reduction in capsular porosity within 3 days of exposure to BSS (fluid challenge). Even though the baseline porosity was significantly different in the two groups (3.00 ± 0.5 μL/min and 29.67 ± 12.12 μL/min, p < 0.001), the effect of passage of BSS was similar. Capsular porosity fell by approximately 80% in both groups from baseline after single BSS challenge. Capsular thickness was significantly less in Advanced Eye Center (AEC) rabbits at baseline. There was no change in the capsular thickness before and after single fluid challenge. Conclusion: Passage of BSS at physiological pressures for under 40 minutes caused marked reduction in the porosity of the fibrous capsule within 3 days. This was not associated with any significant thickening of the fibrous capsule within this time frame.