"Neri" is the function name, what is used for well-melt of fibre when for scooping. Sometimes it's easily misunderstood, the Neri is not adhesive, it works as a dispersant. Neri is highly viscous, but no glueing. The artisan mixes fibre and Neri in the vat. For the moment of scooping, Neri keeps an average density of fibre. The scooped wet paper is laid over and over, but not bonded. After scooping, the overlapped hundreds of paper is pressed for dewatering. At this time, the ingredient of Neri is mostly discharged. The root of Tororoaoi(トロロアオイ=Sunset Hibiscus) is the most popular Neri. But it doesn't work well at high temperature, roughly said the limit is 15 Celcius.
For Gampi paper and clay mix paper, the bark of Nori-Utsugi (ノリウツギ=Hydrangea Paniculata) is more effective and works also in summertime. It's available only in the wild. Nowadays, it is getting very hard to find.