I thought all welting had to be bias cut as well or it wouldn't lie right around the curves....but I am not an upholsterer...
I would love to find someone like you found....and also would love to know what online fabric source you used.
Linda C

I know upholsterers on both sides of this debate. One I use locally (30+ years experience) says he does not. Others say it lies better on the curves.

I think it depends upon the stretch in the fabric, if any. Some fabrics stretch one way and not another; some stretch only on the diagonal. Another consideration is if you want a "candy stripe" or "barber pole" effect or are trying to align strips, for example across the outside arm, through a welt, down a skirt. Another that I know matches stripes on the welt, even for curves in cornices.

For a small amount of welt, it can be wasteful of material or you can end up with a lot of short pieces, meaning a lot of seams. For things like chair seats, sometimes you can get enough welt out of the selvage instead of needing additional yardage.

Some fabrics have a directional grain and the upholsterer has to be careful to keep the grain running in the same direction for spliced welt so you won't end up with dark and light shading across the seam.

Thoughts about COM:

By the way, charging more for your own material (COM - customer's own material) is common and is often called a cutting charge. The way I see it that markup on fabric helps subsidize the hourly labor rate of the upholstery shop. Some even have a different hourly rate for COM.

Non-COM also enables the upholsterer to have some control over the quality or material requirements. If something goes wrong with COM, then I think you're pretty much out of luck asking the upholsterer to warrant it. Likewise if you run short on material. Then there is always "which side out?" that has gotten upholsterers into trouble more than once. I don't understand COM too much -- I don't go into a mechanic with a bag of parts.

When I looked at COM on a new piece of furniture, the factory was happy to do it, but the base price I paid was for a medium level fabric piece. So I was essentially paying for the fabric twice, what I bought plus what I paid for for a mid-range fabric but didn't get. I have to imagine COM at the factory slows things down quite a bit in the cutting department.

Thanks. It's good to know it's not "wrong" to not always go with the bias for the welt. There will be plenty of fabric - needs three yards and I've ordered 5. The two places I have ordered from on line are:
Interior mall and Info@fabricsandhome.com

Great point about right/wrong side of fabric. I'm also having a cornice made through a decorator but they are purchasing the fabric directly. That fabric I considered just reversing to use on the chairs but found this other complimentary fabric on-line and could not resist the pattern and the $35 less per yard price.

Thanks again.