You are looking for "TPU". You will see it listed as "TPU 95a", 90 or 85 or something like that. 95a is pretty common to print with because it is mostly plug and play in the X1C, but it is not super flexible. More like a rubber ball hardness than a soft foam.What about soft-ish rubber ? I'd like to do some MAC suppressor wipes
The higher the number after TPU, the harder the material, but if you are making "thick" things you can also play with the infill to adjust the flexibility.
Also, the lower the number the harder it will be to print because it gets squiggly to push through the extruder when it is really flexible.