Liners are different, they just catch any solids, and do not provide additional absorbency, so will not help your heavy wetter. Liners can be paper, or stay dry fleece, neither will work as boosters. Fleece liners just catch solids, they do not add any absorbency. Inserts can be classed as booster pads as they can be layered to add absorbency to any cloth nappy for your heavy wetting child. Silk liners again just provide a liner layer, but can help with rash. A nappy booster is an absorbent layer which makes your nappy absorb more.