Two types of large diameter SiC CVD filaments have been investigated on both chemical and mechanical standpoints: a 100#m filament with a tungsten core (from SNPE) and three 140#m filaments with carbon cores and surface coatings (from AVCO). On the basis of microprobe (X-ray, Auger and Raman), X-ray diffraction and SEM analyses, it appears that the former is made of a single homogeneous stoichiometric SiC deposit while the latter are mainly made of two concentric shells (the inner being a SiC+C mixture and the outer almost pure SIC). All the C-core filaments had received a surface coating (either pure pyrocarbon or SiC+C mixture) presumably to protect the brittle SiC deposit against abrasion due to handling in opposition to the W-core filament which seems to have no surface coating at all. The W-core filament, although smaller in dia- meter, is weaker than the C-core filaments (average UTS of 3 and 4 GPa respectively for a 40 mm gauge length). However, its strength distribution is much narrower (We/bull moduli of 7-8 and 2-5 respectively). Failures of most filaments appear to have a multi- modal character.