Macrovoids in solution-cast membranes: Direct probing of systems exhibiting horizontal macrovoid growth

► Slowly growing horizontal macrovoids (HMVs) are studied in solution-cast membranes. ► Nucleation of primary HMVs occurs near sample edge. ► Bubbles serve as secondary HMV embryos. ► HMV tips grow ahead of the solidification front. ► Stresses affect the direction of HMV growth.