After watching Jeremy @BlackMagicCraftOfficial make some great mats with dollar store products, I made some minor adjustments, and did the same. I've made a 2' x 2', and 3' x 3'. You can really make any size you want, and they're light and FLEXIBLE!
If you like great art, awesome minis, and having fun, check out Relicblade @MetalKingStudio :
https://relicblade.com
https://www.instagram.com/relicblade/
https://www.instagram.com/sean_sutter_art/
Follow me on Instagram: https://www.instagram.com/caffeinatedminiatures/