Optical stack is disclosed. The optical stack includes a first optical stack that includes, a first optical adhesive layer, and a reflective polarizer layer that is disposed on the first optical adhesive layer. The reflective polarizer layer substantially reflects light of a first polarization state and substantially transmits light of a second polarization state orthogonal to the first polarization state. The optical stack also includes a second optical stack that includes a second optical adhesive layer, a low index layer that is disposed on the second optical adhesive layer and includes a plurality of voids dispersed in a binder, and a light directing film that is disposed on the low index layer and includes a plurality of unitary discrete structures. Portions of each unitary discrete structure penetrate into the first optical adhesive layer. Portions of each unitary discrete structure do not penetrate into the first optical adhesive layer. Each unitary discrete structure defines a penetration depth and a penetration base at the interface between the penetrating and non-penetrating portions of the unitary discrete structure. The penetration base has a minimum penetration base dimension. The plurality of unitary discrete structures has an average penetration depth and an average minimum penetration base dimension. The ratio of the average penetration depth to the average minimum penetration base dimension is at least 1.5. The peel strength between the first and second optical stacks is greater than about 30 grams/inch.