"Speedy Jim" wrote
Rather than rigid "pipe" (either L or M), consider using soft
copper tubing. That's available as Type "L" with the same OD (5/8")
as 1/2" pipe. Much, much easier to pull thru tight spaces and
avoids a lot of soldering/torch work inside spaces.

There is also PEX tubing, which is even easier to work with,
but requires special tooling.

I've never used the flexible stuff. I don't know if it's UPC-acceptable?
Therefore, this becomes a question for the homeowner, even when employing a
contractor. If inappropriate, it's best for homeowner to know, and prevent.

Intuitively, I can't imagine why soft, flexible copper would be prohibited.
I would expect it's much more expensive. Isn't this stuff intended for
air-conditioning systems?