# Plastic as building insulation **URL:** \ **Category:** In My Humble Opinion\ **Created:** [August 4, 2023, 7:10pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074 "2023-08-04T19:10:09Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 4, 2023, 7:10pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/1 "2023-08-04T19:10:09Z")
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. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [August 4, 2023, 7:25pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/2 "2023-08-04T19:25:16Z")
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. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 4, 2023, 7:26pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/3 "2023-08-04T19:26:57Z")
Dang. Perhaps it’s used should be limited to government buildings. ---
**Author:** ![Roderick\_Femm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/roderick_femm/32/14875_2.png) [@Roderick\_Femm](https://boards.straightdope.com/u/Roderick_Femm)\ **Post date:** [August 4, 2023, 9:04pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/4 "2023-08-04T21:04:03Z")
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. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 4, 2023, 9:30pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/5 "2023-08-04T21:30:32Z")
Foam insulation can be sprayed between studs in existing construction. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [August 4, 2023, 9:33pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/6 "2023-08-04T21:33:20Z")
If you left them intact and used them as building material instead of insulation, fire probably wouldn’t be as big of a risk. [![](https://world-habitat.org/wp-content/uploads/2019/01/Un-joven-albau00f1il-construyendo-810x495.jpg) ](https://world-habitat.org/wp-content/uploads/2019/01/Un-joven-albau00f1il-construyendo-810x495.jpg) ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 4, 2023, 9:50pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/7 "2023-08-04T21:50:30Z")
I wouldn’t believe they can take a lot of compression. ---
**Author:** ![Roderick\_Femm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/roderick_femm/32/14875_2.png) [@Roderick\_Femm](https://boards.straightdope.com/u/Roderick_Femm)\ **Post date:** [August 4, 2023, 9:59pm UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/8 "2023-08-04T21:59:30Z")
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. ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [August 5, 2023, 12:27am UTC](https://boards.straightdope.com/t/plastic-as-building-insulation/988074/9 "2023-08-05T00:27:37Z")
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.