The dual-layer system on the Zettyo Syngergy is called "Bipolar System", which uses two different material to produce an unique feeling. The outer material of Zettyo Synergy is firm but not hard providing a tight feeling during use. The inside wall are lined with small nubs and large ribs made with another material to provide a stronger/softer stimulation depending on the model you choose. The large inner chamber along with the small entrance allows for great vacuum feeling simply by squeezing air out when inserting.
Zettyo Synergy Yuuna has a series of large ribs and long and short nubs. A choke point near the end creates a strong stimulation. Yuuna has a larger inner chamber than Arisu allowing for a stronger vacuum sensation. Yuuna's "Bipolar System" has a firmer inner layer compared to Arisu.
*Use only water-based lotion or lube with this product.