Hi I think it is from evaporation of plasticizers in the layer. As they evaporate over time, the material shrinks. This causes a void. The void provides another path for the plasticizer to evaporate and a local stress point. This forms the stem like channel feature. As time goes on, plasticizer evaporates from the edges of the channels. This causes new stems to radiate outward. This makes the typical fern leaf look. I would guess the biggest difference between different manufactures is either a different material or different sealing of the edges. The fogging of the material is most likely moisture from the air. Dwight