Door Panel Substrates: Why Most Are PP-TD20

Core requirements of a door substrate

Stiffness comes first: the panel is large and thin, so insufficient stiffness means visible give under hand pressure and squeaks as the door flexes.

Dimensional stability next: the panel carries snap-fits, armrest mounts and speaker openings, and uneven shrinkage makes assembly difficult.

Low odour and low VOC — the most complained-about item in a car interior.

How PP-TD20 performs

Flexural modulus of 2,200-2,600 MPa with shrinkage of 0.9-1.2%, combined with a low-odour mineral formulation, satisfies all three while keeping density and price low.

Where vacuum forming or greater structural strength is needed the spec moves to PP-TD30 or PP-GF20; with higher toughness required, PP+EPDM takes over.

Against the alternatives

ABS offers better stiffness and surface but costs more and weighs more, with no automatic win on scratch or odour; long-glass PP performs better still but sits a clear price tier above.

PP-TD20 therefore remains the mainstream door substrate for mainstream trim levels.