Description

Product Overview

A PP duct rain cap is an injection-moulded polypropylene terminal fitting that fits over the outlet of a PP exhaust duct run. It shields the opening so rain, snow and debris stay out of the duct, and it matches the round PP duct range from φ110mm to φ600mm.

The rain cap is injection moulded in PP or flame retardant PPs, in beige or grey, and joins the duct run by hot air welding, with socket connection reinforcement at the joint. It is fitted as the last part of the run, over the outlet of a roof or wall exhaust duct. For the straight duct this rain cap is fitted to, see Polypropylene Round Ducts.

A duct rain cap is one part of a ventilation system: it protects the outlet of the run rather than connecting or branching it, and matching fittings are available from the same supplier so a complete PP duct line can be specified from one source.

Product Selection Summary

Good Fit

• Roof and wall exhaust outlets that must stay clear of rain and snow
• Exhaust runs where debris could enter the open duct end
• Terminal protection for the outlet of a PP fume or ventilation line
• Projects needing flame retardant fittings for part or all of a run

Conditions To Confirm

• Duct diameter (φ110mm to φ600mm, 11 standard sizes) and quantity
• Material grade: PP or flame retardant PPs
• Gas composition, concentration, temperature and moisture at the operating point
• Whether the outlet also needs airflow backflow protection (use a back draft damper there)

Not a Replacement For

• Fans, airflow balancing devices, back draft dampers or gas treatment equipment

Technical Specifications

Confirmed Product Parameters

Parameter	Value
Product Type	PP Duct Rain Cap (rain cap for exhaust duct)
Material	PP (polypropylene) or PPs flame retardant grade
Size Range	φ110-600mm – 11 standard sizes
Connection	Hot air weld; socket connection reinforcement
Fabrication	Injection molding
Color	Beige / Grey
Working Temperature	-15℃ to 80℃
Chemical Resistance	pH 1-14 (acid and alkali)
Certification	ISO9001, ISO14001, RoHS

Available Sizes (φ)

Diameter	Diameter
φ110mm	φ355mm
φ160mm	φ400mm
φ200mm	φ450mm
φ250mm	φ500mm
φ315mm	φ550mm
	φ600mm

Material & Performance

Because round fittings are injection moulded rather than welded from sheet, the rain cap keeps the same corrosion resistance as the welded duct while offering consistent moulded dimensions, smooth surfaces and a shorter production time for standard sizes.

PP duct rain caps are injection moulded from polypropylene, chosen for corrosive fume handling in ductwork:

• Acid and alkali resistance: PP withstands corrosion by high-concentration acids and alkalis across a wide pH range (pH 1-14).
• Sound insulation: PP reduces vibration and noise transmitted through the fitting.
• Light weight: moulded PP fittings are light and easy to handle and weld on site.
• Consistent moulded dimensions: each size is produced to a standard mould, giving uniform dimensions and wall thickness across batches.
• Long service life: PP duct systems offer a service life of up to 50 years under specified operating conditions.
• Anti-condensation: PP conducts heat poorly, reducing condensation and heat loss at the fitting.
• Wear resistance: the smooth moulded surface resists scaling and deposit buildup, keeping the outlet area clean through service.

Flame retardant PPs is available where fire-rated ductwork is required; specify the required flame retardant grade when inquiring. The material grade applies to the whole fitting, so a single grade can be specified across the duct, fittings and accessories in the run.

Applications

Terminal Protection for Exhaust Outlets

Rain caps are fitted over the open outlet at the end of an exhaust duct run, where the duct passes through a roof or an outside wall:

• Roof exhaust outlets – protecting the vertical outlet from rain and snow
• Wall exhaust outlets – shielding the horizontal outlet at the building face
• Fume and ventilation terminals – keeping debris out of the last section of the run
• Outdoor duct ends – reducing water entry where the duct is exposed to weather

The rain cap is the last part of the run, so it does not affect airflow balance inside the duct: it protects the opening while the exhaust stream continues to leave through the outlet.

For an exhaust outlet, the rain cap is welded over the end of the duct after the run is complete, so the fitting is added as the final step of installation. Because the cap is made to the same standard sizes as the round duct range, it can be ordered with the rest of the run and welded on site with the same tools.

Selection Notes & Quotation Information

Rain Cap or Back Draft Damper?

A rain cap protects the outlet of the run from rain, snow and debris entering through the open end. A back draft damper stops airflow moving back into the duct when the system is off. The two protect the outlet in different ways and can be used together: the damper stops backflow inside the duct, and the rain cap shields the opening from weather.

To Quote PP Duct Rain Cap

Provide: duct diameter (φ110-600mm), quantity, material grade (PP or flame retardant PPs), color (beige or grey), application, destination port, and your duct schedule or drawings.

MOQ and lead time are confirmed per project. Request a quote via WhatsApp or email using the contact block below.

Installation & System Integration

PP duct rain caps are joined to the outlet of the duct run by hot air welding, and the joint is reinforced with a socket connection. The same joining method applies to straight duct and other fittings, so the rain cap becomes part of the same welded, sealed system.

Complete systems combine rain caps with straight duct, flanges, couplings and elbows. See the full range of PP duct systems.

Related Products

• Polypropylene Round Ducts
• PP Back Draft Damper
• PP Air Duct Flange
• PP Air Duct Coupling
• PP 90° Elbow
• Full PP Duct Range
• PP Air Duct Guide – a complete guide to PP duct types, sizes and materials.

FAQ

What is a PP duct rain cap?

It is an injection-moulded polypropylene terminal fitting that fits over the outlet of a PP exhaust duct run, shielding the opening so rain, snow and debris stay out of the duct.

What sizes are available?

11 standard sizes from φ110mm to φ600mm: φ110, φ160, φ200, φ250, φ315, φ355, φ400, φ450, φ500, φ550 and φ600mm.

Rain cap or back draft damper – which should I choose?

A rain cap protects the outlet from rain and debris entering through the open end. A back draft damper stops airflow moving back into the duct when the system is off. They can be used together.

How is it connected?

By hot air welding to the outlet of the duct run, with socket connection reinforcement at the joint – the same method used for straight duct and other round fittings.

Is flame retardant PP available?

Yes. The rain cap is available in standard PP or flame retardant PPs; specify the required flame retardant grade when inquiring.

What do I need to provide for a quote?

Duct diameter, quantity, material grade, color, application, destination port, and your duct schedule or drawings.