Plastic as building insulation

I wonder why plastic bottles aren’t washed, shredded and used as insulation. It could be blown in as cellulose was in the 1950s and 60s, or heat formed into bats to fit between 16" or 24" studs.

Plastic is a fairly poor conductor of heat, so that’s good for something that you want to use for insulation. However, plastic is also flammable, which is very bad for something used inside of your walls. Worse, burning plastic (at least the type used in plastic bottles) creates some rather nasty toxic fumes, which would make a potential fire even worse.

Dang.
Perhaps it’s used should be limited to government buildings.

By the way, they still blow cellulose (or something) into walls in certain circumstances (I’ve seen it on This Old House). If you have uninsulated exterior walls which require no work (inside or outside) except insulation, blown insulation is the easiest way to do it.

Foam insulation can be sprayed between studs in existing construction.

If you left them intact and used them as building material instead of insulation, fire probably wouldn’t be as big of a risk.

I wouldn’t believe they can take a lot of compression.

True. I wonder if it would require more holes (because maybe it wouldn’t fall down into the cavity before it started to set) or if they have specific formulas of foam for that purpose.

I was speaking of the bottles layered with mortar in the picture.
Blowing cellulose and foam: My in laws house was foamed. They drilled holes from the outside between studs, pumped in the foam and sealed the holes with plastic caps. Interestingly, Mrs. Plant worked for the foam guys, and overheard contractors say it was easier to pump if they changed the mixture. Easier to pump, but offering less R factor.