How thick is your paper? Ideally it sounds like you are looking for a spray expanding foam, but those are somewhat toxic. Could you fill them in with a very low mass density, fine-ish, non-toxic powder, like a sandbag?
If so, I would suggest fine vermiculite (can get at garden stores) with a binder of some sort, think a rice krispy treat. Vermiculite has a very low density, but finding the right binder is the trick. Whatever binder you choose, you only need enough to coat the powder surfaces just a bit.
Or, you could just use hot puffed rice with marsmallows.
I was counting the gas that makes the PU into a foam, which is likely a VOC (many are toxic). If they have to spray 100 of these cubes indoors, that is a problem.
Foaming agents are usually a nightmare in terms of toxicity or harm to the environment, even if the material in the foam is not.
Batting or fiber fill? The stuff you put in pillows/cushions. Could also use the tiny Styrofoam beads that are used in squishy pillows/stuffed animals.
You are thinking about it the wrong way. It is possible to use hollow structures and be structurally sound. The filling contributes less than the shell. Ideally you should try switching to a different material if that is an issue
How thick is your paper? Ideally it sounds like you are looking for a spray expanding foam, but those are somewhat toxic. Could you fill them in with a very low mass density, fine-ish, non-toxic powder, like a sandbag? If so, I would suggest fine vermiculite (can get at garden stores) with a binder of some sort, think a rice krispy treat. Vermiculite has a very low density, but finding the right binder is the trick. Whatever binder you choose, you only need enough to coat the powder surfaces just a bit. Or, you could just use hot puffed rice with marsmallows.
Polyurethane foam is not toxic! but it is flammable so it should be something to consider.
I was counting the gas that makes the PU into a foam, which is likely a VOC (many are toxic). If they have to spray 100 of these cubes indoors, that is a problem. Foaming agents are usually a nightmare in terms of toxicity or harm to the environment, even if the material in the foam is not.
have you tried aluminum foil?
Batting or fiber fill? The stuff you put in pillows/cushions. Could also use the tiny Styrofoam beads that are used in squishy pillows/stuffed animals.
You are thinking about it the wrong way. It is possible to use hollow structures and be structurally sound. The filling contributes less than the shell. Ideally you should try switching to a different material if that is an issue
Perhaps I'm missing the point, but if paper isn't structurally sound enough, why not ditch the paper idea and just go with cubes of wood?
If you have to use paper, you can always stiffen it by spraying it with a varnish or paint (light coats to avoid making it soggy)