I've found them to be superb grips-THE most ergonomic grips of their type. They seem to be made of a material that's midway between rubber and nylon in its formulation and characteristics. I have a set for my Security Six that Jacques Trausch amicably modified for me (twice) as a sort of a beta-test. I can't recommend them highly enough-they may not be the best looking (think "industrial utilitarian/functional"), but ergonomically and performance-wise they're excellent.
See
www.trausch.com
Best, Jon