PVA revisited (2021-02-22)
My initial experience with PVA was poor. The paper was strong, but it had a plastic character that made the folds unfold. Since then, I have realised that diluting PVA reduces the problem considerably. The dilution depends on the brand of PVA you have and the requirements of the model you want to fold. This is also the case with all sizing agents, including methylcellulose.
Conclusion: PVA is useful if you dilute it enough.
I have folded a simplified version of Sipho Mabona's elephant using diluted PVA and double-tissue (30 cm):

You can use PVA with other sizing agents to solve various problems. For example:
- The sugar present in some sizing agents makes the paper brittle. A bit of PVA will solve the problem.
- Some sizing agents become less crisp when the ambient is humid or if your fingers have some moisture. This is the case of potato starch and to a lesser extent of gelatine. A bit of PVA solves the problem.
- It improves egg-white power double tissue making it close to methylcellulose double tissue.

Last meaningful update: the 26th of February 2021
Index of sizing agents