Insulating the Sash weight Cavity

I would think that fiberglass would be about the least likely to cause you any allergy problems, at least compared to any foam insulation that would have chemicals or blown-in that would stir up dust. I'd just make sure he cuts it and does as much of the handling outside and perhaps passes the bats through the window at the point they will be used rather than carrying them through the house.

Spray urethane.

Fiberglass is easier though. I don't know of anyone allergic to it. If you handle it, you can get itchy. Sealed in the window, it is far less reactive than any other material for insulation. Ed

What kind of insulation is in your walls and attic?

IMO, since there is a certain size space for every window, I would suggest put the Fiberglas into a 'tube' of polyethylene, roll the ends and staple them, and bring them in and put them into the sash weight space. You would not have an allergic response to it, but you can still have dermal sensitivity to Fiberglas if you touch it. After all, it is spun glass fiber. And there is potential carcinogenicity if it's inhaled.

You can have a sensitivity reaction to fiberglass but you can't be allergic to it. Alternatives are filling the cavity with an expanding foam (but than can be tricky) or you can use something like the preformed foam roles used to insulate pipe. Oher possiblities are rock wool (also itchy) and if you can seal the cavity at the bottom and sides you could use pour in cellulose insulation.

Fiberglass does not cause allergenic reactions! It may cause reactions that appear like allergenic reactions. Having allegories will not increase your likelihood of having a problem.

While there are down sides to fiberglass, over all it is one of the safest of materials to use.

Strips of styrofoam would work, but check on whether it could cause a problem by generating toxic fumes if there's a house fire, though there won't be much of it in there.

Jeff

You could use cotton batts instead of fiberglass batts. Check out

Cheers, Wayne

Cotton would be more likely to create problems because it can support mold.

Cotton insulation is treated with borates as a fire retardant and mold/pest inhibitor.

Wayne