Dale Sirkle wrote an answer about Sorel 1964 Pac T Boot - Men's on December 18, 2010
I just replaced a 25 year old or more pair of Canadian made Sorel's for a new Chinese pair because the tread wore down smooth. To be fair the new outer boots seem to be of good quality (time will tell), but the inserts are much thinner than the originals even though they are all rated at 9mm thickness. The Canadian made inserts are 30% thicker than the Chinese inserts. I had bought extra inserts for my old boots and had like new ones to put in my new boots. The old ones were rated at only -10f. The inferior Chinese ones are rated at -40f. The old inserts are much warmer than the new ones.