1. What does “ISO” mean?

ISO is the general industry term for isocyanates used in polyurethane (PU) foam.

Main isocyanates:

TDI – Toluene Diisocyanate

MDI – Methylene Diphenyl Diisocyanate

Both react with polyols to make PU foam.

2. TDI (Toluene Diisocyanate)

Key characteristics

Very reactive

Produces soft, flexible foam

Lower viscosity (easy to process)

Strong odor, more volatile

Mainly used for

🛏 Flexible foams

Mattresses

Sofa & cushion foam

Pillows

Carpet underlay

Why manufacturers use TDI

Excellent softness & elasticity

Lower cost (traditionally)

Fast production cycles

⚠️ Notes

More health & safety concerns

Mostly used in slabstock (block foam)

Less common today in some regions due to regulations

3. MDI (Methylene Diphenyl Diisocyanate)

Key characteristics

Less volatile than TDI

Stronger, more durable foam

Can make rigid, semi-rigid, or flexible foam

Higher viscosity

Types of MDI

Polymeric MDI (PMDI) – rigid foam, insulation

Pure MDI – molded flexible & semi-rigid foam

Mainly used for:

🏠 Rigid foam

Building insulation

Sandwich panels

Spray foam

🚗 Molded foams

Automotive seats

Armrests

Headliners

👟 Footwear

PU soles

Why manufacturers use MDI

Better mechanical strength

Lower emissions vs TDI

Wider application range

4. TDI vs MDI – Quick Comparison

Feature

TDI

MDI

Foam type

Flexible only

Rigid, flexible, semi-rigid

Odor

Strong

Low

Volatility

High

Low

Safety

Higher risk

Safer than TDI

Typical process

Slabstock

Molded / spray / rigid

Cost

Lower

Higher

5. Why “ISO” choice matters

Choosing TDI vs MDI affects:

Foam softness or hardness

Processing method (block vs mold)

Emissions & regulations

Product durability