Commercial silicone o-rings are highly vulcanized, rubber-like formulations made from peroxide-cure silicone or what the industry calls "gum." They're highly vulcanized in order to achieve a lot of industrial strength for myriad commercial uses. Herbie's Audio Lab, however, formulates superior platinum-cure silicones that are loosely cross-linked (not highly vulcanized or cross-linked), which results in less strength but much more absorption of micro-vibration, specifically formulated and tweaked for home audio applications only.
Silicone o-rings are a cheap trick and used frequently to control vacuum tube microphonics, but they are only marginally effective. The silicone itself, being highly vulcanized and rubbery, has some resonance issues that affect sonic linearity, at worst causing bloopy bass and/or higher-frequency attenuation or false emphases. At best, they accomplish some microphonics control but the sonic results are usually mid-fi at best, achieving some benefit but at the cost of some detriment.
An enclosed o-ring of any material has no outlet to release excess vibrational energies other than to reverberate them right back to the vacuum tube glass. Herbie's damping instruments, on the other hand, are "C" shaped, with the open ends of the ring allowing vibrations to simply dissipate to the surrounding atmosphere and assimilate within the C-ring itself without forcing the vibrations back to the tube glass, to which all the internal tube parts are directly or indirectly coupled.
We have lots and lots of customers who have replaced silicone o-rings with Herbie's vacuum tube damping instruments for improved results. Never any mention that the o-rings did as well or better; Herbie's dampers are virtually always a "keeper" in this regard. Some tube gear manufacturers, Conrad-Johnson and Audio Research for instance, include cheap silicone o-rings on some of their component vacuum tubes. This is often better than nothing, but not sufficient to really bring out the best potential of the tube gear. According to feedback we've gotten from customers, representatives of both C-J and AR have recommended upgrading their own silicone o-rings with Herbie's Audio Lab damping instruments.
Our experimentation and auditions with both silicone o-rings and Teflon-coated silicone o-rings has indicated that these products might not really be worth the bother. You don't want trade-offs with your audio reproduction, only improvements, to whatever degree.
Steve HerbelinHerbie's Audio Lab