Apparatus and methods for manufacturing and repairing fibre-reinforced composite materials are disclosed. In various embodiments, the apparatus and methods disclosed herein use a resin retaining/releasing device comprising resin having a viscosity that is temperature dependent for infusion into a region of a part. The resin retaining/releasing device may include a first sheet and an opposite second sheet at least partially enclosing the quantity of resin. The first sheet and the second sheet may be gas-permeable. The second sheet may be substantially resin-impermeable when the viscosity of the resin is above a threshold viscosity and resin-permeable when the viscosity of the resin is below the threshold viscosity.