OutdoorGearLab

If comfort is a top priority, the Rapha Trail Knee Pads are a tremendous choice. These pads are incredibly comfortable thanks to an excellent fit and quality materials. The RHEON Lab armor patch is fairly large and provides excellent mid-duty protection, and it conforms nicely to the kneecap and remains comfortable hours into a ride. The consistent fit is secure and these pads stay in place whether you're grinding up a long climb or charging back downhill. We feel these are a great pedal-friendly option for riders who seek a little more protection than the more minimalist pads provide.
While Trail Knee Pads do breathe well enough, the overall length of the sleeve is quite long. On warm or hot rides, these pads can feel quite toasty. A set of pads that don't cover so much of your leg will inherently allow for better airflow. They are also on the more expensive end of the spectrum, though we feel that the price is justified by the impressive blend of comfort and quality. 
Read more: Rapha Trail Knee Pads review

Best for Most

pinkbike.com

We love most elements of these knee pads. One area that could use some improvement is the level of ventilation. For a mid-duty knee pad, they are a little clammy. The sleeve is tightly knit with a relatively thick material that doesn't let much heat escape. The all-fabric construction may also be prone to ripping or tearing more easily in the event of a crash compared to pads armored with plastic or rubber. 
Read more: Dakine Slayer review

Budget Pick

amazon.com

powerreviews

If you are seeking maximum protection, the 7iDP Project Knee are the mountain bike knee pads for you. They have the most robust padding in our test, and the long, heavy-duty sleeve provides additional leg coverage and protection. The impressive quality of the construction really stood out to us. These pads use tougher and thicker materials than the other pads in our test, giving them a robust built to last feel. We do not doubt that these pads can take a beating and are an excellent option for hard-chargers, shuttle monkeys, and even some bike park rats. Considering all the protection they offer, we also found them to be surprisingly comfortable with a great fit. 
While we love the Project Knee pads, they have a somewhat limited bandwidth. They are not a very pedal-friendly option; there is a lot of bulk, and the materials are so thick that they are quite warm. It seems that climbing and ventilation were not a priority in the design process; getting radical was. These pads are also quite expensive, but we feel the quality, performance &#40;within the intended application&#41;, and durability are impressive enough to warrant the cost for the right rider.
Read more: 7iDP Project Knee review

Knee Pad Comparison