The welt seam is similar to the mock flat felled seam but generally has just one row of topstitching. This is less bulky than the flat felled seam. It works well for thicker fabrics that do not fold well for the felled seam method.
Where is a welt seam used?
This seam works well for thick and/or bulky fabrics to provide more strength to the seam. It is generally used for straight seams. It reduces bulk in shoulder seams on a thick wool coat or side seams for a straight skirt or pants.
It’s also a good choice for fabrics that tend to ravel easily, like a loosely woven linen. By edge finishing the seam allowance and then securing it with a top stitch, the seam is sturdy and resists raveling.
How is this seam different than a flat felled or mock flat felled seam?
The welt seam has one row of topstitching and exposed seam allowances, similar to the mock flat felled seam. The mock flat felled seam has two rows of topstitching to make it look like the flat felled seam. The flat felled seam has no seam allowances exposed. The raw edges as they are all wrapped inside one of the seam allowances before topstitching.
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