Home Guy wrote:

I'm at the home despot today (here in canada) and I'm wondering how much
copper pipe is costing (on a per pound basis) as a multiple of the going
market rate for copper (about 4 - 4.5 dollars per pound).

So I'm looking at 12-foot, 1/2 inch copper pipe.

I see some for $24, and some for $13.69. One is labelled "LX", the
other as "MX".

They look and weigh about the same.

I figure a 12-foot piece weighs about 2 lbs (maybe 3 tops?) so there's
about $8 or $9 worth of "raw" copper in these pipe sections that are
retailing for $14 to $24 each.

But what's the difference between this LX and MX marking?

Wall thickness. There are types K, L and M in order from thickest wall
to thinnest wall. If you have "aggressive" water that corrodes pipes,
the L will last longer, if your water isn't a problem, the M is cheaper.
Type K isn't normally seen in regular plumbing use. There is definitely
a weight difference between types, but you won't readily notice it by
hand.