The 661 EVO Knee Guard uses D30 material to absorb and disperse the energy created by an impact. The molecules in the D30 material are soft and flexible but lock together if you crash. The greater the force of the impact, the more the molecules lock together and the greater the protection.
I have several rides on these and they have been excellent. They are light weight and offer great protection without being uncomfortable or effecting your pedaling. The D30 material is a proven compound.
I've had a few crashes on these. My knee is perfectly fine however my thigh wishes it had padding. I've had them for over a year and they still look almost brand new. I usually don't climb with them on, but I have. Fairly comfortable, perfect if you don't want plastic guards.
These are very comfortable pads, I've been able to ride for hours without any uncomfortable rubbing. I've only had a few "opportunities" to test them out, but they've saved my knees each time. Pretty lightweight, breathe awesome, would recommend them to anyone.