Or sleeping bag? Or boots/hat/gloves? It is always a tough question to field from a customer. All of these items are insulation that have relative values. Different customers have different standards of what is warm. Most sales people try to dodge the question. But some retailers allow the customers to decide for themselves.
At Alewalds in Stockholm Sweden, they installed a cold room to allow customers to check the product out for themselves.
I have seen these in the US in the past, the REI Denver store used to have one as did the Eddie Bauer in Bellevue, WA.