These are not an official Cornish Milk product but they do have permission from Joe & Reece (The Cornish Milk Guys!). We are currently sourcing packaging to create an official line of testers but due to shortages (thanks to the 'P') we are not sure of the time frame. So, Joe & Reece have kindly let me create my own little tester jars. I've had one of these glass jars filled with water and stored upside down for the last 3 weeks with no leakages or evaporation - the sellers description said 'airtight' and they weren't lying!