You may want to explore Foss Shape. There are several instructional videos on Youtube regarding it. There is still some debate as far whether the material is inert but you can place a barrier such as muslin between your helmets and the Foss Shape.
Here is one instructional video:
https://www.youtube.com/watch?v=ZlVPimbJfSg&index=3&list=PLN_6WQmT6nTav1e2GCVpoR1imqOjtmcgV
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