A Comprehensive Analysis of Inspection and Certification Standards for Shoe Products: A Quality Control Guide from Size to Seam Line

April 3, 2026

I. Size Inspection
During the size inspection process, the inspectors must ensure the following points:
The sizes of both left and right feet are marked identically: The size markings for the left and right feet of the same pair of shoes must be the same.
Actual size consistency: The actual size (length) of the shoes is the same, and the sizes of the upper and midsole patterns are also the same.
Criteria for judgment: Incongruence in size is considered a major defect, as it affects both wearing and sales.
II. Gluing Inspection
Gluing is a common quality issue in footwear. During the inspection process, strict control is necessary:
Limit for glue peeling of finished shoes: No glue peeling areas longer than 2mm and deeper than 1.5mm are allowed.
Bonding strength: The outsole is firmly bonded to the upper surface, with no cracks or gaps.
Tensile test: The bonding strength must exceed 2.5 kilograms per square centimeter.
Criteria for judgment: Excessive delamination beyond the limit is considered a major defect, while failing to meet the tensile strength requirements is a fatal defect (affecting safety and usability)
III. Damage Inspection
The inspector needs to thoroughly examine the damage conditions of all parts of the footwear:
Part Standard Requirements
Front and side of the shoe head, front protective eye display surface No damage is allowed
Inner side of the midsole and other non-display surfaces Damage area should not exceed 2 square millimeters
Back collar opening and tongue No damage is allowed
Needle sewing area No broken stitches are allowed
Tongue label No damage is allowed
Outsole Insufficient material length exceeding 1mm and width 1.5mm is considered unqualified
Shoe laces Defective laces are considered unqualified
Judgment Criteria: Damage on the display surface is a major defect; Excessive damage on non-display surfaces is a major defect; Damage on the outsole and laces is a major defect.
IV. Rigidity Test
Rigidity is a crucial item in the certification of footwear products. During the inspection, the following components need to be checked:
Shoe tongue fixation: Must be secure and must not come off.
Webbing fixation: Must be secure and must not come loose.
Molding, trademarks, letters: Must not fall off
Attention: Must be firmly attached and must not come off.
Transferred or embroidered size: Must not come off.
Component rivet lines: Firmly attached, must not come off.
Metal fasteners: Any cracks, deformations, loosening, missing bottom parts, or peeling paint are all considered non-compliant.
Snap fasteners: If they are not secure or prone to breaking, they are considered non-compliant.
Outsole label: Failure to secure properly - non-compliant
Sole assembly: Failure to meet the standard for layer separation
Criteria for judgment: Any detachment or loosening is considered a major defect, as it affects the product's service life and safety.
V. Color Difference Inspection
Color difference directly affects the appearance of the product and its market acceptance. The inspectors must conduct a strict comparison:
Shoe side symmetry: Symmetrical parts of a single shoe sole, symmetrical parts of the entire pair of shoes for both left and right feet, must be color-matched
Outsole: There should be no color difference between the outsoles of the left and right feet; there should be no color difference at the edges of the outsoles; the patterns on the outsoles can have a slight color variation.
Accessories: The trademarks, ribbons, drop molding, electro-embossing, high-frequency, and printing must not have significant color differences.
Judgment criteria: A significant color difference is considered a major defect. Any defect that seriously affects the appearance should be judged as unqualified.
VI. Inspection of Thread Lines
The quality of thread lines directly reflects the craftsmanship level of shoes. The inspection standards are as follows:
Project Non-conformity Circumstances
Needle Carriage Damage Any damage to the component of the needle carriage makes it non-conforming.
No Bottom Line Any absence of the bottom line results in non-conformity.
Drop of Needle When the needle carriage drops the needle, it is non-conforming.
Double Thread Loose connection, repeated stitching, tangled thread, severely uneven line spacing, and unsmooth stitching are all non-conforming.
Loose Bottom Line Loose force-bearing parts and main components of the bottom line are common, and the surface thread protrudes, resulting in non-conformity.
Edge/Needle Spacing Severe unevenness, unsmooth lines, and significant impact on appearance are all non-conforming.
Thread Color Left and right foot thread colors are inconsistent, and the color of single needle/double needle thread is incorrect, making it non-conforming.
Judgment Criteria: Any of the above issues constitutes a major defect.
VII. Sampling and Decision Rules
1. Sampling Plan
Determine the sampling quantity and acceptance level based on the AQL (Acceptable Quality Limit) standard.
For key items such as tensile testing and the limit of glue separation, it is recommended to adopt a special inspection level.
2. Defect Classification
Defect Category Definition Judgment Criteria
Fatal Defect Insufficient tensile strength, severe loosening of metal fasteners, delamination of the outsole Zero tolerance. Any defect found will result in the entire batch being deemed non-compliant.
Major Defect Sizes not matching, excessive cracking, excessive damage, component detachment, obvious color difference, severe poor stitching quality Judged according to AQL standards
Minor Defect Slight color difference (background pattern), slight thread ends, packaging flaws Judged according to AQL standards
3. Inspection Report
All inspection results must be recorded in the official inspection report.
Including measured data, defect photos, and tensile test results
Clearly define the conclusion and recommendations

VIII. Linkage between Factory Audit and Certification
1. Supplier Capability Assessment
During the factory audit, footwear suppliers are required to conduct a focused assessment of:
Size control process and inspection equipment
Adhesive bonding process and tensile test records
Material Inspection and Damage Control Process
Method for testing the assembly firmness of components
Color difference management (standard light source box, color matching technician qualification)
Quality control and inspection frequency for the vehicle line process
Qualifications and Training of Inspectors
2. Product Certification Requirements
For footwear products to enter different markets, they must comply with the corresponding certification standards:
Target market Certification requirements Inspection focus
Chinese market GB/T 15107 "Tourist Shoes", GB 30585 "Safety Technical Specifications for Children's Shoes" Physical and mechanical safety, chemical safety
European market REACH regulations, EN 14700 series Hexavalent chromium, prohibited azo compounds, phthalate esters
American market ASTM F963 (for children's shoes), CPSIA Small parts, lead content
During inspection, it is necessary to verify the consistency between the product label and the certification certificate.
3. Continuous improvement
Any quality issues discovered during the inspection should be promptly reported to the supplier.
Repetitive issues need to be followed up and rectified through factory inspections.
Establish a quality traceability record to support product certification audits