A series of high density ceramic composites with carbon fibre content between 40 and 65% and ultra-refractory ceramic matrix was produced by slurry infiltration and hot pressing. The matrix consisted of ZrB2-10 vol% SiC or ZrB2-40 vol% SiC ceramic mixtures. Water-based and polymer-based routes were tested to analyse the effects on microstructure, mechanical properties and oxidation resistance at 1650 degrees C in air. Changing the process and/or the processing parameters was found to affect the final composition, the amount of residual porosity, the matrix/fibre adhesion. Composites with nearly fully dense matrix and optimized infiltration of fibre preforms were found to possess the highest strength (240 MPa) and oxidation resistance. Composites with weak interface and higher porosity in the matrix showed higher toughness (up to 12 MPa m(0.5)) but were more prone to oxidation and erosion. (C) 2016 Elsevier Ltd. All rights reserved.