Will this bag fit size 12 boot plus a knee...
Will this bag fit size 12 boot plus a knee brace along with helmet etc?
While 4200 cu. in. isn't the best description of bag size I can tell you that this product has interior dimensions of 20 x 15 x 14 inches. In addition to this the lower portion of the bag is designed specifically to hold snow sport boots. I would recommend measuring your gear, and using the dimensions you gather, to see how they will best fit inside of the bag.
without a doubt i would say yes. i have size 14 boots, helmet, pants, jacket, multiple pairs of gloves and goggles, multiple hats, and assorted crap. there is so much room in it, i find myself not cleaning it out often enough because everything fits. so now i have random crap like stickers, old lift tickets, and socks i don't wear in there.