Polycarbonate Clear Plastic Sheet 12" X 18" X 0.0625" (1/16") Exact, EasyRuler Film, Shatter Resistant, Easier to Cut, Bend, Mold than Plexiglass. VEX Robot, Hobby, DIY, Industrial. Glass Replacement

Another issue - do you have a lid on the betta tanks? Bettas are notorious for accidentally jumping out of their tank (just see these many posts): http://reddit.com/r/bettafish/search/?q=betta+jumped+out&cId=cdb796f0-f812-439a-9d8b-a9ad087074cb&iId=51d74e4a-8eb5-4ddd-97d3-c87e1f8f3fbe If you do not have a lid, I advise you to look into getting or making one ASAP.https://www.amazon.com/dp/B07MQTDF4R - great for DIY tank lids for smaller tanks 5-10 gallons.