I don't recall having heard of Tundra before finding them while surfing the net but they seem to have an interesting range of sleeping bags.
Tundra bags are made in Warsaw, Poland by 'Warmth Unlimited' and are tested by Leeds University which should mean their temperature ratings are comparable to those of Alpkit and possibly PHD.
The thing that attracted my attention was the 'Ethical' tag, there's been some discussion about the various methods of collecting down, plucking down from live birds being quite controversial. It seems not all the bags are made using 100% ethical down, the figure of 95% is given for some of the range but certainly 96% is a vast improvement over other less ethical down collection methods.
The website is worth a look but unfortunately for the gram counters there doesn't appear to be any indication of the weights.
There is a link to a UK supplier, Tundra Stockists