Our firmness levels are set by our silicone manufacturer according their hardness scale, also known as shore. They provide this handy chart :)
We currently offer 3 levels of firmness :
Shore 00-20 : Super Soft
This is very soft and yielding, feels similar to a gummy candy.
Shore 00-30 : Soft
This is soft and squishes easily with hand pressure, feels similar to a gel insole.
Shore 00-30 : Medium
This is our firmest, squishes with firmer hand pressure and offers stability, feels similar to a rubber eraser.
There are many factors that can may a toy feel more or less firm, thicker toys will have less squish and feel firmer.
In addition if the silicone was manufactured or mixed at colder temperatures this can also make the end product feel slightly firmer.