Good pants. One of the better pants out there. They used to be the best. The Levi's 501 set the bar. Not any longer. Now it's made in Mexico.  I've even got a pair made in Haiti. No longer the best, but still better than most.

As a kid, we used to buy only Levi's. Back then, they were made right here in the old USA, and they were the best. My folks used to take us kids over to the Levi's building on Valencia Street, and we bought directly from the factory. Today's Levi's just don't measure up to what they used to be.

Get an old army surplus wool blanket.
Lay out jeans and trace a pattern about 2 inches larger along the entire outline.
Cut & sew together into a pair of ugly, green pants with an opening for the fly.
Flip your jeans inside out.
Insert jeans into army blanket pants.
Sew army blanket pants to jeans at the hem & waist.
Flip jeans right side out.
Wear.

You've just made a pair of insulated jeans that's better than anything lined with flannel.  Wool blanket lined jeans.  Nobody sells them.  Nothing store bought will be warmer.