4 ms·To nit, they are typically made of metalized BoPET, not actual Mylar.by georgeg23 3y agoTo nit, they are typically made of metalized BoPET, not actual Mylar.j-bos 3y agoWhat is BoPET?neom 3y agoBoPET is polyethylene. Metallised BoPET is polyethylene + (usually) aluminum. https://en.wikipedia.org/wiki/BoPET https://en.wikipedia.org/wiki/BoPET https://en.wikipedia.org/wiki/Metallised_film https://en.wikipedia.org/wiki/Metallised_film