Use this handy guide to determine what model you'll need. The range is geared towards different disciplines so start with that and then check tyre and size requirements.
From here you'll need to identify your rim internal width and tyre measurements. Check your bike, wheel or tyre manufacturers website for this info if you don't know it. Knowing these numbers is important as it's possible you have an Ebike but rims too narrow to fit the EDH or a Trail bike with tyres to large to fit the Original insert.
17-25mm Rims and 33c-45c Tyres? Rimpact CX is your choice.
20-30mm Rims and 1.5"-2.35" or 40c-55c Tyres? You can choose either Gravel/XC or CX depending on how close to the middle of their range you fall, there is some overlap where both will work well
25-35mm Rims and 2.35"-2.6" Tyres? Rimpact Original or Pro fit your set up. Now the choice is based on discipline and how hard you are on your wheels.
30-45mm Rims and 2.4"-3.0"Tyres? The Rimpact EDH is the right tyre insert for you. If you are rocking a 2.4" tyre be aware that fitting these inserts will be a challenge.