1.The Essentials: Three Inputs Create a “Melt-Processable Rubber”
Long-chain diol (polyol)
Forms the soft segment: elasticity, low-temperature flexibility and rebound. Its chemistry governs water,
oil and weather resistance.
Diisocyanate
Combines with the chain extender to form hard segments: strength, modulus and heat resistance. Its type
affects light stability.
Short-chain extender + additives
Often BDO. Ratios, catalysts and stabilizers tune hardness, reaction behavior and durability.
Polyaddition
Soft segment
Rubbery continuous phaseHard segmentPhysical crosslinkElongation and reboundHard segmentStrength and shape retention
Soft segment
Soft segmentFlexibility at low temperature
Microphase separation gives TPU rubber-like elasticity. On heating, hard-domain associations weaken and the
polymer flows, enabling repeated thermoplastic processing.
2 | How TPU Resin Is Made: Polymer Synthesis Is Not Part Shaping
One-shot route
Short process; suited to continuous production
Meter all three inputs together
Polyol + diisocyanate + chain extender
Intensive mixing and reaction
Reaction and chain growth occur together
TPU melt
Sequence control depends strongly on metering, mixing and temperature
Prepolymer route
Two-stage reaction; greater sequence control
Make an NCO-terminated prepolymer
Polyol + excess diisocyanate
Add the chain extender
Build a more defined hard-segment sequence
TPU melt
More control steps; performance is not automatically superior
Reactive forming
Reactive extrusion or casting onto a belt line
Curing and cooling
Complete reaction and stabilize morphology
Pelletizing and screening
Produce commercial resin pellets
Moisture-proof packaging
Dry before downstream processing
3 | How TPU Is Classified: One Grade Belongs to Several Categories
A. By soft-segment chemistry | Environment and feel
Mechanical strength, oil/solvent resistance, abrasion and adhesion
A Use caution in hydrolytic and microbial environments
+ Hydrolysis/microbial resistance, low-temperature flexibility and rebound
A Lower oil/solvent resistance and, in some systems, heat-aging performance
Polycaprolactone TPU
+ Balanced abrasion, strength, rebound and hydrolysis resistance
A Higher cost and fewer commercial options
Polycarbonate TPU
+ Hydrolysis, heat-oxidation, weathering and long-term durability
A Higher cost; confirm the processing window for the specific formulation
B. By diisocyanate | Light and color stability
Aromatic (commonly MDI)
Mainstream, strong and economical. Tends to yellow under UV/light, so it is better suited to dark-colored
or indoor parts.
Aliphatic / cycloaliphatic
Better non-yellowing, color retention and optical clarity. Usually more expensive; used for optics,
protection films and appearance-critical parts.
C. By hard-segment content / hardness | A continuous spectrum
Soft: Shore A range
Flexibility, elongation, cushioning and low-temperature bending
More hard segment-
Hard: Shore D range
Higher hardness, modulus, load capacity and heat-deformation resistance
| How Pellets Become Parts: Processing Method Also Defines the Grade
Injection-molding grades
Footwear parts, wheels, seals and structural parts. Key factors: flow, release, shrinkage and cycle time.
Extrusion grades
Tubing, cable jackets, profiles and monofilaments. Key factors: melt strength, dimensional stability and
surface quality.
Film / calendering/ blow-molding grades
Films, sheets, synthetic leather and bladders. Key factors: gauge stability, clarity, bonding and weathering.
Special-process gradeswindow
Powder, 3D printing, foams and adhesives. Key factors: particle size, melting, crystallization or foaming
Common prerequisite: TPU absorbs moisture. Dry it according to the supplier’s TDS before processing to
prevent bubbles, splay, degradation and loss of mechanical performance. Do not rely on a single
‘universal TPU” temperature, time or dew point.
Process
5 | Selection Logic: Environment First, Then Appearance, Mechanics and
1Service environment
Water / cold start with polyether. Oil/ solvents /adhesion start with polyester. Long-life, balanced
durability – evaluate polycarbonate or PCL
2 Light and colorand verify its UV rating.
For transparent, light-colored or outdoor non-yellowing parts, start with an aliphatic/cycloaliphatic system
3 Mechanics and feel
Specify Shore A/D together with tensile, tear, compression set, rebound and abrasion. Hardness alone is
not enough.
4 Processing and compliance
Choose a grade designed for injection, extrusion, film or another process; then verify MFR, drying, flame,
food/medical and regulatory documents
Grade-name warning:”B = polyester” and “E polyether” are not universal industry rules each supplier
defines its own codes. Compare the soft-segment chemistry, dlisocyanate system, hardness, processing
route and certifications in the TDS/SDS.
Soft segment/ soft-segment families
Hard segment/ hardness
Synthesis route
Part processing
Post time: Oct-09-2026