the most simple way to explain butted tubes is this the tubing walls are thicker where needed for strength (i.e, joints). and thinner else where as in the middle of the tube. double-butted is as it implies,meaning two inner tube wall thicknesses and so on for triple and even quad butted tube sets. mostly seen in steel framed bicycles.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
Typically with a quality tube set butted style tubes would be lighter. some as much as 30% over straight gauge. You have to have the thickest part of the tube @ the joints . this is where the frame is stressed the most. So if your tube is .075 thousandths and straight gauge. it runs the whole length of the tube. Where as the butted tube @ .075 can be only .035 thousandths for 90% of its length which is where the weight savings come in to play. The thickest part of the tube is only and inch or so to the joints. The variables would be how the tubes are attached to each other that also plays a role in overall weight, i.e. lugged, fillet,welded, bonded. and lastly how the tubes are designed for certain ride characteristics the manufacturer is trying to achieve.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
you probably guessed, Steel of course, however I have vintage bonded lugged alloy and carbon fiber road and Mtb that are very dear to me too.
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"