It depends on how tight or lose you like to wear your pants when squatting but one can purchase squat pants that the manufacturers guarantee will increase your 1RM. It depends on whether you are a competitive powerlifter or a bodybuilder, the squat pants are made from the same heavy duty material as seen in a squat suit used by powerlifters.
Many bodybuilders use lycra type tights to get that feel and the stretch that spandex or other polyester type fabric. The stretch whether you wear tight or lose pants is important as you need to always make sure that your leg muscles have room to move and will not feel confined in pants that don't allow lateral movement.
The option of purchasing squat pants should only come after you have tried various other types of training pants to squat in. The same can be said for investing in an expensive squat suit which should be preceded by trying different types of other squatting options like lycra tights etc.
You are more than likely very aware that adding any squatting accessory to your squat could easily land up developing into a bad habit so if you do train in squat pants you should always get someone who knows how to squat to take a look at your form to see if everything is OK.
Clothing for hard training sessions should not be taken lightly and one should always rather invest in some cheap lycra tights before you spend a lot of money on squat pants. If you feel that you could lift a heavier weight if you had more stability in your hips and groin area then squat pants may be a good idea.
Many bodybuilders simply squat in basketball shorts or some other tracksuit material that can easily stretch to accommodate the pump in your legs that you should get if you are squatting correctly. Simple track pants with lycra tights underneath them is commonly used by many bodybuilders.
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