A squat bar pad is a tool used in weightlifting to support the spine and prevent it from flexing backward. These are attached to weight plates and usually rubberized for comfort purposes.
It's most commonly used by powerlifters, but can also be useful for other athletes, such as those in gymnastics and Olympic weightlifting. A squat bar pad can be purchased online or in a training store at https://www.amonax.com/products/barbell-pad-for-squat-and-hip-thrusts-black.
An adjustable one will make it easier to purchase the right size for your lifter. The Barbell Warehouse offers a number of squat bars; the majority are rubber-coated, but some have been coated with latex. The latex-coated models are less likely to bleed, but also tend to be more slippery when wet.
Squatting on the heels with a flat back and hips fully extended results in no forward flexion of the spine, which is why you don't need any kind of bar pad for squats. However, if you're going heavy and you feel pain from improper spinal alignment, the bar pad can help reinforce proper positioning.
Remember to keep the bar over your mid-foot. If you're using racks or power cages to squat in, you may need to add weight to the bottom of the bar. I like a 2-5 pound plate on each side, depending on how heavy I'm working out and my goals for the workout. This will ensure that the bar doesn't roll off the clamps during your descent.
In order for squats to be effective training for strength gains, you must learn the proper form in which to perform them. There are many different variations of squats, but all of them have one thing in common: The movement is initiated by a rapid descent from an upright position.