The wet sponges (like the baby sponge) are packed in a bag after being dropped in a weak sterilizing solution of Bardac 2240. This is a weak solution of medically tested antibacterial. It is not held by the sponge at all when rinsed as it is totally water soluble and washes clean away upon rinsing.
Hope that helps! (Of course the dry sponges do not contain any of this which is why we prefer the dry sponges.)