Anything that is 100% polyester will keep bub feeling dry. When you test your fleece are you just wetting it with nothing under it? The idea is the liquid will go through it & into the absorbant layers but the wet feeling wont pass back through to bubs skin.
The fleece on your bought nappies might be a better quality fleece then what we can get at SL. Also there might be a build up of washing detergent on them which will repel the water also. You may like to try a strip wash but using a small drop if "Dawn" dishwashing liquid in a HOT wash & then rinse twice. Thats how I do it anyway.

Try putting two layers of your SL fleece over the top of a booster then wet it if you push down on it you should find your hand will stay reasonably dry but the thing with SL fleece is its prone to compression leaks so if you haven't got your nappy boosted well then you may still find you will get leaks when bub is sitting for long times like in the car/pram etc.
When I was using pockets from SL fleece I found they worked well if I boosted with either a hemp or flannel teamed with microfibre. The microfibre will draw the wee away quickly then the hemp or flannel will absorb what gets squished out of the microfibre as its not good at holding on to the wee if its squished. KWIM??