KAM plastic snaps are industrial grade so are intended to have a strong closure.
When you open snaps, you pull the material that they are attached to apart. So the weaker your material, the harder it will feel to pull apart.
For example, size 20 snaps open without difficulty with sturdy material like vinyl. But they will feel very hard to open on thin cotton, because the cotton is weak.
For that reason, we recommend reinforcing thin, stretchy, or delicate material with a sturdier, non-stretch fabric prior to installing the snap.
Size 16 plastic snaps can also be used in lieu of the more common size 20 because they are smaller and have a relatively gentler grip. Do note you should still reinforce with size 16.
If you have already attached your snap to your project, opening and closing the snap several times will help to loosen it just a bit. Gripping the fabric closer to the snap when you pull them apart will help to reduce the strain on the fabric. It's also been suggested by some of our Facebook group members that rubbing wax / beeswax / zipper glide sticks on the snaps can help.