All three sizes are made of the same material and in the same style. The material is a very strong and durable waterproof non-breathable plastic. With a thicker separate piece on the base for improved durability and shape.
All the top are secured with the popular dry bag “roll and clip“ method which has been proven to be very good at remaining sealed. All three liners have the same “stealth 25mm“ clips securing them, i think thee clips are the perfect size as unless you have ridiculously bulky gloves on the are easy to undo, although doing them back up can be difficult when the liner is fully packed, it is not a real issue. One issue although is unless carefully packed there is sometimes a lot of air left inside the liner, although not a major issue a lot of people do prefer to remove as much air as possible, in my opinions it is certainly a sacrifice worth making in exchange for absolute waterproofing. Of course all the bags are also suitable as flotation devices.
The main Bergen liner is 120 litres (almost big enough to roll up and sleep in! But i'm only 5'8“) and to over come the difficult of a “roll and clip“ top on a larger size the plastic top is in two pieces. Both pieces have rounded edges to reduce the chance of the liner being pierced. The main liner is the perfect width for the bergan and sit neatly inside, i foudn when fully extended it just protrudes from the top of the draw cord type section of the bergan. I found that simply due to the size of the liner when the top is fastened the material folds and creases, this will probably lead to an increased rate of wear but under testing is still waterproof.
The third is a 50 litre rucksack liner which is a perfect for a generous sized day sack or smaller Bergen.
These bags are not yet available online so I'm not sure of the prices but my guess is that the full Bergen set would retail around £40-50 and the day sack liner around £25. For this you get as much of a guarantee of dry kit as you're ever going to get and a 5 year warranty!