Bifenthrin: the repellent termiticide (Biflex, HomeGuard)

Bifenthrin is a repellent synthetic-pyrethroid termiticide used to form the chemical part of a termite management system on Australian residential work. It is the active ingredient in the widely used products Biflex and HomeGuard, and it works by creating a treated zone that termites detect and avoid, rather than by killing the colony through transfer (verified 2026-05-25, industry and APVMA sources). It is APVMA-registered and applied only by licensed pest-management technicians at label rates.

What it is

Bifenthrin is a synthetic pyrethroid, a lab-made analogue of the natural insecticide pyrethrin found in chrysanthemum daisies. In termite use it is strongly repellent to termites but virtually odourless to people, which is part of why it became a default for residential pre-construction work. It also binds strongly to soil (a high soil-affinity, Log Kow around 6.0), so it tends to stay where it is applied rather than leaching away, which is what underpins its long service life.

The two products a builder will hear named most often:

Biflex (FMC): the soil-applied bifenthrin termiticide, used for chemical soil barriers.
HomeGuard (FMC): the bifenthrin-treated system, including a chemically treated sheet (a physical-plus-chemical product) classified under AS 3660.3 and registered with the APVMA.

Both carry long-running manufacturer warranties backed by residual-efficacy studies.

How it works: a repellent barrier

Bifenthrin is a repellent termiticide. The treated soil or sheet forms a zone that foraging termites sense and turn away from. On contact it has a fast knockdown, killing termites quickly. The practical effect is a deterrent perimeter: termites are pushed to look for an untreated gap rather than tunnel straight through.

That repellent behaviour has a direct consequence for how the barrier must be built. Because termites actively seek a way around a repellent zone, the treated barrier has to be continuous and complete. Any untreated gap, a missed penetration, a break at a pipe, a join that was not lapped, becomes the path the colony finds. A repellent barrier with a hole is worse than it looks, because the termites are actively probing for that hole.

Bifenthrin versus fipronil

The other dominant termiticide active in Australia is fipronil (the active in Termidor and similar), and the two work in opposite ways:

	Bifenthrin (Biflex, HomeGuard)	Fipronil (Termidor and others)
Mode	Repellent: termites detect and avoid the zone	Non-repellent: undetectable, termites tunnel through
Colony effect	Fast knockdown, kill on contact at the barrier	Slower “transfer effect”: termites carry the active back to the colony
Barrier logic	Must be continuous; a gap is an entry point	Termites pass through and pick up a lethal dose
Typical label life	Up to 10 years (longest on the market)	Up to around 8 years

Neither is simply “better”. A repellent like bifenthrin gives a long-lived deterrent perimeter and the longest label life available; a non-repellent like fipronil aims to knock the colony down by letting termites pass through and spread the active. The choice is the pest technician’s call based on the situation, the site, and the management plan. What matters for the builder is understanding why the install detail differs: a repellent barrier lives or dies on being unbroken.

Where it fits in the build

Bifenthrin most commonly appears as a pre-construction chemical soil treatment or as a treated-sheet system, forming part of the termite barrier required for the building. The chemical barrier is one option among several (physical barriers, treated-sheet systems, stainless mesh, graded stone); bifenthrin is the chemical-soil and treated-sheet route.

It does not stand alone. The chemical barrier works alongside the rest of the AS 3660 system, including the termite inspection zone (the exposed slab edge that keeps any bridging visible). A bifenthrin barrier under the slab plus a maintained inspection zone above it is the common belt-and-braces residential setup.

The NCC requirement behind it

Bifenthrin is not used because a builder likes it; it is used because the National Construction Code requires termite risk management. NCC 2022 Volume Two calls for a termite management system to protect the primary building elements of a Class 1 building in areas where termites are a known risk, and it names AS 3660.1 as the deemed-to-satisfy path (verified 2026-05-25, ABCB NCC 2022 Housing Provisions). A bifenthrin chemical soil treatment or a HomeGuard treated-sheet system is one acceptable way to meet that AS 3660.1 obligation. The Code also requires a durable notice to be fixed in the building (commonly in the meter box or under the kitchen sink) recording the system installed, its date, and the inspection regime, so the next owner and the next pest technician know what is protecting the structure.

Compliance and who applies it

AS 3660 series. Termite management for new building work sits under AS 3660.1, with soil-treatment application and treated-sheet assessment covered across the AS 3660 parts. The treated-sheet products are assessed under AS 3660.3.
APVMA registration. Bifenthrin termiticide products are registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA), the federal regulator for agricultural and veterinary chemicals. Using a product outside its registered label use is not compliant.
Licensed application only. Soil and chemical termite treatments must be applied by a licensed pest-management technician at the rates and methods on the product label. It is not a builder DIY item, and a treatment certificate from the licensed applicator forms part of the building’s documentation.

For a builder

Coordinate the timing. A pre-construction soil treatment has to happen at the right point in the slab sequence; book the pest technician into the program rather than chasing them at the last minute.
Protect the barrier. Once a repellent barrier is down, treat it as live: do not trench through it, bank fill over a treated edge, or breach it at penetrations without the applicator reinstating it.
Keep the paperwork. The applicator’s treatment certificate (product, active, concentration, area, date) is part of the compliance record and the durable-notice obligations for the build.
Brief the client on the lifespan. A 10-year label is long, but it is not forever. The homeowner still needs ongoing annual inspections, and the barrier will eventually need renewal.