An innovative alternative to packaging milk could be a threat to the carton let alone the pint bottle.
The dairy wants to reduce the amount of plastic they use
Carmarthenshire organic dairy co-operative Calon Wen's initiative supplies milk in polythene bags which can be transferred to reusable jugs.
Should the paks replace polybottles completely, it could reduce the amount of plastic used by nearly 100,000 tonnes each year, the dairy said.
The paks are being stocked by Waitrose in Abergavenny, Barry and Monmouth.
Whitland-based Calon Wen comprises of 20 organic family farms across Wales producing milk and butter.
One of them, Iwan Jones said: "The eco pak uses 75% less plastic than a one litre milk polybottle and also an empty eco pak takes up a fraction of the space of that of an empty polybottle.
"To give you an idea of what that means, you can fit 75 empty eco paks inside a one litre polybottle" he said.
Elen Morris, also from Calon Wen, said people in Canada had 40% of their milk through similar paks.
A variation of the eco paks were used in the seventies, but the reusable jugs was a new initiative, Ms Morris added.
She said the jug costs £1.99 and a litre of the organic milk costs 91p.
The eco paks are due to be rolled out across the UK.