Low Melting Point Yarn (LMPY), technically classified as a bicomponent or co-polyamide/polyester filament, is a thermoplastic bonding agent used to provide structural rigidity and localized reinforcement in footwear uppers. Unlike standard high-tenacity yarns, LMPY features a sheath-core or solid structure that melts at temperatures between 85°C and 110°C. During the heat-setting phase of shoe production, the yarn liquifies and fuses with surrounding structural fibers, creating a stabilized, 3D-shaped composite. This process replaces traditional chemical stiffeners and heavy TPU overlays, significantly reducing total component weight while maintaining tensile strength and dimensional integrity.
Strategic Shift in Footwear Reinforcement
The transition from traditional multi-layered assembly to integrated 3D knitting has necessitated a shift in reinforcement materials. Conventional methods rely on solvent-based adhesives and manual placement of internal reinforcements, which increase labor costs and VOC emissions.
By incorporating Flying Shoe Materials directly into the knitting program, manufacturers can engineer "stiffness zones" (such as the heel counter or eye-stay) without secondary bonding processes.
Direct factory supply of GRS-certified low-melt filaments.
Request Technical Data Sheet & Bulk Pricing
Technical Specifications: Material Performance Data
The selection of LMPY denier (D) and filament count (F) is contingent upon the required gsm of the knit and the desired shore hardness of the final product.
| Parameter | PA Low Melt Yarn | PES Low Melt Yarn |
| Melting Point | 85°C - 105°C | 110°C - 130°C |
| Common Specs (D/F) | 50D/12F, 75D/24F, 150D/48F | 100D/36F, 150D/48F, 300D/96F |
| Tenacity (cN/dtex) | ≥ 3.0 | ≥ 3.5 |
| Boiling Water Shrinkage | ≤ 5% | ≤ 8% |
| Bonding Strength (N/cm) | 45 - 60 | 40 - 55 |
| Application Zone | Toe box, Heel counter | Mid-sole bonding, Side panels |
3 Core Engineering Advantages
1. Weight Reduction and Minimalist Design
Integrating 150D Low Melting Point Yarn into the knit structure eliminates the need for 0.5mm - 1.2mm TPU hot-melt films. This reduction typically saves 15g to 30g per shoe, a critical metric for high-performance marathon and sprint footwear where energy return and mass are inversely correlated.
2. Controllable Hardness and Elasticity
The modulus of the shoe upper is adjusted by varying the feed rate of the LMPY. High-density insertion in the heel counter provides the necessary 85-90 Shore A hardness required for stability, while low-density blending in the forefoot maintains the 35% elongation required for natural metatarsal flexion.
3. Streamlined Thermal Processing
LMPY activation occurs during the standard 120°C - 140°C heat-setting cycle. The hot-press bonding duration (typically 15-30 seconds) ensures the polymer flows evenly through the fiber interstices, achieving a peel strength exceeding the 40 N/cm industry benchmark for Tier-1 footwear brands.
Process Parameters for Material Engineers
To ensure optimal bonding without degrading the primary carrier yarn (e.g., high-tenacity polyester), the following parameters must be strictly monitored:
Pre-heating: 80°C (3-5 minutes) to initiate molecular vibration.
Active Bonding: 115°C - 130°C (depending on PA vs. PES base).
Cooling Phase: Rapid cooling to below 40°C to lock the 3D geometry and prevent crystallization brittleness.
FAQ
Q1: What is the MOQ for customized denier specifications in Low Melting Point Yarn?
Our standard MOQ for stock specifications (50D, 75D, 150D) is 100kg. For custom-engineered melting points or specialty dope-dyed colors to match specific brand palettes, the MOQ is 500kg per specification.
Q2: Does your yarn comply with Oeko-Tex and GRS sustainability standards?
Yes. All WithTech low-melt filaments are Oeko-Tex Standard 100 certified (Class I). We also provide GRS (Global Recycled Standard) certified versions made from post-consumer recycled (PCR) chips, accompanied by a valid Transaction Certificate (TC) for every batch.
Q3: Can LMPY be used in water-repellent (DWR) treated uppers?
LMPY provides effective bonding even on DWR-treated fibers, provided the surface tension of the carrier yarn is not below 30 mN/m. For extreme hydrophobic treatments, we recommend a pre-production bonding test to verify peel strength consistency.
