AFAIK, Lafuma is (but, nowadays, who knows?) a french company, at first mainly known for its backpacks and other camping gear.
It has expanded its products range to shoes, clothes, sleeping bags and hunting gear (see also "Millet" - more technical gear, for climbing etc..- or "Le Chameau" - hunting gear - those brand names are now in the same Lafuma Group).

their web site

I can try to find independent reviews of a specific product and translate it, if you are interested.

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If you look for instance at the "Warm'n light 1kg down" sleeping bag, you will see the following explanation (see what others ie Chris K have said in other posts) :
"Lafuma sleeping bags are laboratory tested by the independent agency IFTH (1) in compliance with French standard G08-013. This standard determines the following three usage temperatures:
- extreme temperature: experienced users (2) feel cold. Hypothermia risk for inexperienced users after a few hours.
- comfort temperature limit: experienced users (2) feel neither warm nor cold. Inexperienced users may suffer general discomfort.
- comfort temperature: inexperienced users (3) do not suffer any discomfort, even local, from the cold.
Remember that the conditions, the user's training and physical condition at the time of use can create discrepancies in these measurements, and consequent coldness.
Notes :
(1) French Textile-Clothing Institute
(2) Experienced users adapt their position inside the bag to the ambient conditions.
(3) Inexperienced users do not necessarily understand how to use their bag well."