Sources:

Population of the USA

https://www.census.gov/topics/population.html

33% of Americans planning to purchase a costume for Halloween

https://nrf.com/insights/holiday-and-seasonal-trends/halloween/halloween-data-center

40% of costumes are only worn once

https://issuu.com/hubbubuk/docs/hubbub_2017.10.19_sew_spooky_press_

Average costume weight (348g)

We weighed 10 costumes and took an average then compared this to the results of the study below 

http://www.fairylandtrust.org/wp-content/uploads/2018/10/Halloween-Plastic-Clothing-Report-2018-Fairyland-Trust.pdf

Zombie Weight

Weight of an average American man

https://www.cdc.gov/nchs/data/nhsr/nhsr122-508.pdf

Costumes are 90% plastic

http://www.fairylandtrust.org/wp-content/uploads/2018/10/Halloween-Plastic-Clothing-Report-2018-Fairyland-Trust.pdf