Seam Allowance
Seam allowance is the extra width of textile added outside the pattern’s finished line, used for sewing pieces together and finishing edges.
Definition and role
Seam allowances are the parts attached to the outside of the finished line on the pattern (the reference line that will determine the shape of the finished product after sewing). They are necessary for sewing the cut textile together, and after sewing, they become the inside of the seams or the edges that are finished.
The width of the seam allowance is determined based on the design, the thickness and elasticity of the textile, the sewing method, the likelihood of fraying, and the sewing equipment used. It is important not only to specify the width itself, but also to provide instructions so that all parties involved can handle it according to the same standards.
Positioning in product development
In typical product manufacturing, after considering the design and specifications, seam allowances are set during pattern making. Since the process then proceeds to grading, marking, roll, cutting, and sewing, the design of the seam allowances affects the precision, workability, and fabric usage of subsequent processes.
Patterns distinguish between finished lines and cutting lines, and include notches, notches, and grain lines as needed. In sewing, the cutting lines and notches are used as a guide for sewing, so unclear seam allowance settings and indications can lead to dimensional errors and differences between left and right sides.
- The shape before adding seam allowances is checked using the finished line as a reference.
- The cutting line is the outer circumference line, which is the finished line plus the seam allowance.
- Areas with different seam allowance widths will be clearly indicated in both the pattern and the specifications.
Practical aspects of setup and procedures
The seam allowance should be determined for each seam, taking into account the required strength, ease of sewing, seam thickness, and edge finishing method. Areas with strong curves, corners, and openings may be difficult to handle with a uniform width, so consideration should be given to the shape.
In the prototyping stage, the garment is sewn with the specified seam allowance, and the fit of the outer surface, seam strength, thickness, fraying, and any discomfort when worn are checked. If any modifications are made, the pattern, specifications, and cutting instructions are synchronized to ensure that no old versions remain on-site.
- For thin or easily textile, check the required amount, including how to finish the edges.
- In areas with thick fabrics or many overlapping sections, check the thickness when the seam allowances overlap.
- For knits and stretchy textile, check for stretching of the seams and waviness of the seam allowances.
- When working with pattern, check the relationship between the amount of extra fabric needed for pattern matching and the seam allowance.
Points to note regarding ordering and quality control
textile order quantities are calculated based on the pattern cutting lines. Changes to seam allowances affect fabric usage and marking efficiency, so the required textile quantity should be reconfirmed when making changes. In particular, if there are constraints on textile width, pattern direction, nap, or grain, consideration should be given to allowances.
Quality control involves checking for insufficient seam allowances, variations in width, incorrect cut placement, and twisting or pinching of seam allowances. Even if the finished dimensions are correct, improperly finished seam allowances can lead to fraying after washing, cracked seams, and surface fading.
Differences from similar terms
A pattern refers to the entire template that shows the shape and reference lines of each piece of hardware that makes up a product. A seam allowance is the extra portion added to that pattern and is not the same thing. A specification sheet is a document that shares instructions for seam allowance width, sewing method, finishing method, etc.
The grain direction is the reference point for arranging hardware relative to the warp and weft directions of the textile, while bias refers to using the textile diagonally. These are design conditions related to cutting and elasticity, while seam allowances have a different role as the extra amount needed for sewing.
FAQ
Do all seam allowances need to be the same width?
It's not necessary to make everything the same width. The width should be set according to the shape of the area to be sewn, the edge finishing, thickness, strength, and sewing equipment. However, if the width differs from place to place, the width and finishing method should be clearly stated in the pattern and specifications to avoid confusion during the cutting and sewing process.
Will changing the seam allowance affect the amount of textile ordered?
This may have an impact. Widening the seam allowance increases the cutting area for hardware, which can change marking efficiency and required fabric quantity. The impact is more pronounced with pattern matching, directional textile, and narrow textile widths, so recalculate the fabric requirements with the modified pattern before confirming the order quantity.
What are some common problems that can arise from insufficient seam allowance?
This can make it difficult to hold the textile in place during sewing, leading to seam detachment, fraying, seam allowance pinching, and dimensional inconsistencies. It also reduces the amount of space needed for edge finishing and ironing, so it's crucial to confirm during the prototyping stage whether the required amount of work for the sewing specifications can be secured.
