Micrometer sized capsules are often used as single entities for the encapsulation and release of active ingredients, for example in food, cosmetics, and drug delivery. Important parameters that determine the stability of capsules and the release of reagents contained in them are the dimensions and composition of their shell. Most capsule shells are rather thick, thereby occupying a significant fraction of the capsule volume, or they are rigid, making the capsules fragile. This work introduces viscoelastic capsules with very thin shells of order 10 nm. Despite the thin nature of these shells, they are flexible, self-healing, yet, for practical applications impermeable even to low molecular weight substances. These shells are formed by ionically crosslinking surfactants that are functionalized with catechol-derivatives. This work investigates the influence of the number of chelators contained per surfactant and the crosslinking ion on the rheological properties of the membranes and relate it to the mechanical properties of the resulting capsules. This work demonstrates that these shells are impermeable to molecules as small as 340 Da even if loaded with cell culture media, indicating their potential for biomedical applications.