I would say you're interested in polyethylene, polypropylene, of polytetrafluoroethylene.
But you would need to describe the conditions further to be absolutely sure. For example, polypropylene will resist most solvents at room temperature, but there are a fair amount of organic solvents that will dissolve polypropylene at elevated temperatures.
If you can get yourself a copy of the Polymer Handbook, I would suggest looking there for a solvent/non-solvents table.