Filling the Hollow Stock of Spring/Nitro piston

[Bullo oka]

Recently I disassembled the 2 week old NX100 Polaris,
Because the brown stocks colour peeling off (exposing the black colour) and thats because of the gun resting on wood support while shooting (already shot one box of 500 round head and half of 500 flat head). And I decided to respray it with matt black.

The reason for this post is while disassembly I removed the butt pad and found out that the stock is hollow inside and was wondering what if I fill it with something before Reassembly.
Managed to collect some unused (cotton fiber cushion whatever it is called, attached the image)
So, is their any alternative to fill that with, checked on google but those expanding foam, I dunno what that is and where to find it.
If you guys did something with those hollow stock please suggest me.
I have no problem with weight gain, and the reason for the filling is for sound deadening.

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[Gunner_dh]

If weight is not a constraint I believe glass pudding can be an option as it will take the shape as desired only con I can think of would post it gets dried you will have to replace it.
Also artificial clay which is used by children in nursery classes can be another option.

Regards
dh

[Bullo oka]

If weight is not a constraint I believe glass pudding can be an option as it will take the shape as desired only con I can think of would post it gets dried you will have to replace it.
Also artificial clay which is used by children in nursery classes can be another option.

Regards
dh

Thanks gunner for the suggestion, BTW I already packed it up with some iron weight folded with cotton fiber, maybe next time I detach it I'll try those.

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[Gunner_dh]

[emoji106]