Carbon fibers coated with various types and amounts of very high molecular weight silicones (780 000 g/mol) are used to make unidirectional PMR-15 polyimide composites. Coating conditions have been found to affect the fiber arrangement within the interlayered composites which consequently has a strong effect on composite properties. The effect of variation of the type and the amounts of the silicone on the impact resistance, toughness and mechanical properties of the composite is determined. Retention of properties of the thermally aged composites has also been studied. Finally, the interlayered composites are checked for improvement of microcracking resistance.