As an alternative material to aluminum-lithium, cryotanks developed from fiber reinforced composites can offer significant weight savings in applications for fuel containment of liquid oxygen and hydrogen. For composite materials to be accepted and utilized in these structures, they must be resistant to microcracking. It is the objective of this work to develop a matrix system for aerospace composites that alleviates all forms of microcracking from cryogenic cycling regardless of the lay-up and configuration. This will be accomplished by using a novel chemistry that provides the necessary inherent network and backbone structure for this environment combined with newly developed nano-modifiers. This technology and approach will result in a high performance matrix system that has low or no cure shrinkage combined with very low CTE and extremely high toughness. Such a matrix will be combined with carbon fibers to fabricate lightweight, high performance composites that are expected to have the microcrack and permeability resistance required for cryotank structures.