My Alpaca blanket arrived (10 days to arrive) and while not a comparison with a sleeping bag (still to be done, I have done a little test with a Dutch Army blanket.
The Dutch Army Blanket is 1.56m x 2.3m weighs 2.9kg and cost , I think, about £12 from Endicotts, plus P&P which I can't remember but it was a fair amount because of the weight, but certainly it was all less than £20 all in.
The Alpaca blanket is 1.6m x 2.2m weighs 0.68kg and cost £63, inc carriage from
http://www.great-gift-ideas-etc.com/category/alpacablanketsthrows/
Pricing is complicated, and in fact I could have got it for 10% less than this.
The first thing that you notice is how small and light the Alpaca blanket is.
A comparison picture is here
The Alpaca blanket is obviously the yellow one !!
To try and and idea how they performed, I place two identical hot water bottles with 300mls of hot water under each blanket and measured the temperature drop about every 15 minutes. The Ambient temp was 20c and the starting temp for both hot water bottles was 53c.
The temperature drop is shown here:
The hot water bottle under the Alpaca blanket fell to ambient temp after five hours.
The hot water bottle under the dutch army blanket fell to ambient temperature after six and half hours.
While the temperatures were falling, the Dutch army blanket kept the hot water bottle 1 to 2 degrees warmer than the Alpaca blanket. But the Dutch Army blanket is 4.25 times heavier and at least 4 times bulkier than the Alpaca blanket.
Of course this is only one sample, and I'm not entirely sure how this relates to the blankets performance in use, but considering the Alpaca blanket is a quarter of the weight and bulk of the Dutch army blanket, it seems to perfrom rather well. Its also about four times the price as well of course.
Graham