E
xceptional mechanical properties of single-wall carbon nanotubes (SWNT) have prompted intensive studies of SWNT composites. However, the present composites have shown only a moderate strength enhancement when compared with other hybrid materials . Although substantial advances have been made 10 , mechanical properties of SWNT-doped polymers are noticeably below their highly anticipated potential. Pristine SWNTs are well known for poor solubilization, which leads to phase segregation of composites. Severe structural inhomogeneities result in the premature failure of the hybrid SWNT/polymer materials. The connectivity with, and uniform distribution within the matrix are essential structural requirements for the strong SWNT composites . Here we show that a new processing approach based on sequential layering of chemically modified nanotubes and polyelectrolytes can greatly diminish the phase segregation, and render SWNT composites highly homogeneous. Combined with chemical crosslinking, this processing leads to drastically improved mechanical properties. The tensile strength of the composites is several times higher than that of SWNT composites made by mixing, and approaches values seen for hard ceramics.The universality of the layering approach is applicable to a wide range of functional materials. Successful incorporation of SWNT into a variety of composites should be possible, imparting them with the required mechanical properties.SWNT composites are typically prepared by blending, in situ polymerization and extrusion.After extensive surface modification,such as grafting or polymer wrapping , the phase segregation from a macromolecular matrix is smaller than for pristine SWNT, but still remains high owing to vastly different molecular mobilities of both components.For that reason,most common loadings of nanotubes in the polymer matrix are within the 1-15 wt% range, whereas more than 50% of the SWNT content is needed for materials with special mechanical performance without compromising the homogeneity of the composite at the nanometre level. The phase segregation between dissimilar