Personally I would stick with Paraffin, Mineral Oil or Baby Oil rather than a vegetable oil like Sunflower Oil. Oils that eventually evaporate do what you want. The idea is, the sponge being expanded so there is more gas in the pores of the sponge. Whereas, with something like sunflower oil, the sponge will expand, the Oil will be absorbed by the sponge, but it will be liquid oil in the pores, not gas.
Pouring water on the sponge wil also expand the sponge. But I wouldn't use it to boost either.
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