2020–2021 Audi A4 S-Line / S4 B9 Rear Diffuser – Pre-Preg Dry Carbon Fiber

Give the rear end of your Audi A4 S-Line or S4 B9 a sharper, more aggressive finish with this pre-preg dry carbon fiber rear diffuser. The 3D-contoured design adds depth and dimension to the rear bumper for a performance-inspired, high-end look.

Build

• Material: Pre-preg dry carbon fiber — the resin is pre-impregnated into the weave under controlled conditions before autoclave curing, giving exceptional strength with lightweight performance, a consistent weave, and a lighter finished component than standard wet carbon
• Manufacturing: Autoclave cured, precision 3D-contoured for accurate fitment
• Surface finish: Deep high-gloss clear epoxy finish that enhances the carbon weave clarity and protects against UV exposure and surface wear
• Configuration: Single-piece diffuser for the lower rear bumper

Design & Aerodynamics

• Aggressive stance: 3D-contoured diffuser profile adds depth and dimension to the lower rear for a more planted, performance-focused rear end
• Carbon aesthetic: Refined dry carbon weave and high-gloss epoxy finish deliver premium contrast against the factory paint
• Factory-style integration: Precision-molded to the contours of the factory rear bumper for a clean, seamless fit

Fitment

• 2020–2021 Audi A4 S-Line B9
• 2020–2021 Audi S4 B9
• Fits the A4 S-Line and S4 factory rear bumper only — not compatible with the standard non-S-Line A4 or aftermarket bumpers

Package Contents

• 1 × pre-preg dry carbon fiber rear diffuser
• Mounting screws for installation

Installation

• Screw-mounted: Secures with the included mounting screws for a secure, rattle-free fit
• Drilling required: Screw fixing pierces the bumper, so this is a permanent modification rather than a reversible fit
• Surface prep: Clean and degrease the rear bumper at the fixing locations before installation
• Alignment: Dry-fit and check the diffuser sits centred and even across the bumper before driving any screws
• Professional installation recommended for correct positioning, panel alignment, and a clean finish

Before You Install

• Confirm your car is an A4 S-Line or S4 B9 (2020–2021) before ordering — this will not fit the standard non-S-Line A4
• This is a permanent, screw-mounted fitment — dry-fit and confirm placement carefully before driving any screws, as holes cannot be undone
• Take care when parking rear-in — lower rear panels sit close to kerbs and parking blocks