Nittaku Finezip is the best if you want to apply REAL booster.

I found that it alters the feeling of impact depending on if you apply booster over wbg or directly to the sponge, at least for hurricane rubbers. Direct to sponge is great for feeling your blade clearly on every stroke, boosting over wbg generally gives a more elastic feel and greater sense of dwell time at the expense of some speed.

I prefer boosting directly to the sponge, but I've heard boosting the glue layer supposedly helps to delay bubbling and preserves the boost effect for longer. I haven't been able to confirm this though.

merlin el mago wrote: I'm looking to buy 1L WBG to boost the rubbers, I want to know your experience about what WBG is the best to boost the rubbers?

I don't know if there are any places to buy a 1L container of wbg, but I agree with chop4ever. Nittaku Finezip works wonderfully to hold boosted rubbers onto blades. DHS #15 glue is a good alternative as well, and dries into a harder, less elastic layer of latex than Finezip does. 

Between the two, I would choose DHS #15 if want a more direct feeling and Finezip if you want the more spin potential with a slightly softer touch. It's a very subtle difference though, both glues are fantastic.

I usually apply booster directly to sponge. Wouldn't absorption be hindered if a layer of glue is spplied first due to the wbg forming some sort of a barrier/layer for the booster to penetrate? 

My guess is that the booster saturates the wbg layer and gradually permeates into the sponge. Boosting over a wbg layer takes a much longer time to dry than boosting directly to the sponge. The doming effect is also much more pronounced and takes longer to uncurl when boosting over wbg, maybe because of the slower release of the booster through the wbg layer.