AbstractRecently it has become possible to control the internal stresses in fiber composites by the use of special expanding monomers. Carbon fiber‐reinforced epoxy pultrusions have been made in which the epoxy was copolymerized with spiro ortho carbonates. The resulting composites had as little as one third of the usual internal stresses and were tougher than the equivalent carbon‐epoxies made without the spiro. Their tensile strengths and shear strengths suffered no reduction, and there was a slight increase in compression strength in some cases. Water resistance of the composites was increased slightly, and durability in fatigue was much increased by the use of the spiro, probably due to improved adhesion between the fibers and the matrix. Theoretical considerations indicate that the internal shrinkage stress must be controlled at a low value, and not eliminated entirely, for best effects. These controlled shrinkage composites bear the trade name COMACO composites in Can
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