AbstractDye solar cells (DSCs), in their flexible form, are prone to ageing due to ingress of gas as a result of the intrinsic permeability of polymer substrates. Thus, it is important to develop proper encapsulation strategies to limit degradation. Literature on flexible DSCs lacks comparative tests with different permeation barriers, including flexible ultrahigh barriers (UHB). We designed such tests and applied UHBs to flexible DSCs for the first time. We demonstrate that UHBs double the lifetime of cells with respect to those with none or less‐effective barriers. Degradation is due to a combination of electrolyte bleaching, dye detachment, and indium tin oxide (ITO) degradation. The reduced, though still noticeable, performance loss for UHB‐ and glass‐equipped cells can be mainly ascribed to lateral permeation of gas/water, suggesting that efficient solutions for edge encapsulation must be developed to extend lifetimes further.