Sealed unit recycling, explained.

Failed unit, intact unit, triple-glazed, argon-filled — what changes (and what doesn't) when an insulated glass unit hits a recycler's facility.

If you're an installer pulling out warranty failures, a fabricator with a stack of QC rejects, or a glazier clearing the back of the van at the end of a shift — sealed units are the one waste stream that confuses people most. They look like glass. They behave like glass. But they're not glass — not as far as a cullet processor is concerned. There's an aluminium or polymer spacer bar around the perimeter, two layers of edge seal, a desiccant filling the spacer, and (often) a trapped inert gas. Drop one whole into a glass cullet skip and you've contaminated the load.

Below is what actually happens to an insulated glass unit (IGU) once it leaves your site, and what you need to know before you book the collection.

What an IGU actually is

An insulated glass unit is two or three panes of float glass, held apart by a spacer bar around the perimeter, sealed in. The cavity between the panes is what does the thermal work, not the glass itself.

Here's what you're typically looking at:

• Panes. Usually 4mm float, sometimes Low-E coated on the inner face of one or both panes. Could be toughened, could be laminated, could be plain annealed.
• Spacer bar. Either aluminium (older units, still common) or a warm-edge polymer/composite (TGI, Super Spacer, Swisspacer-type products). The spacer holds the panes apart and contains the desiccant.
• Desiccant. Molecular sieve beads inside the spacer, drying out the cavity air so the unit doesn't mist internally.
• Edge seals. Typically a primary butyl seal against the spacer and a secondary polysulphide, polyurethane or silicone seal around the outside edge. That's what keeps the unit gas-tight.
• Cavity fill. Plain dry air, argon, or — for high-spec units — krypton. Argon is the standard now for new build to meet thermal performance targets.

That stack matters when it comes to recycling, because every component apart from the glass itself needs to go somewhere different.

What failed units look like

Most sealed units coming off install vans aren't broken — they're failed. The terminology you'll hear:

• Misted units. Edge seal has gone, moisture has entered the cavity, the desiccant is saturated, and you've got internal condensation that won't clear. The unit still functions as a window, just badly.
• Blown units. Same root cause — seal failure — usually with visible water or chemical staining (the dreaded "tide marks") between the panes.
• Stress-cracked. Thermal shock or installation stress, glass is fractured but the unit is still in one piece.
• QC rejects. Fabricator-side failures — wrong size, wrong spec, wrong toughening, scratch on the inner face. These are usually intact.

From a recycler's point of view, a misted unit and a brand-new unit are processed identically. The fact that the seal has failed doesn't change anything in our facility — we'd be cutting it open anyway.

Why IGUs can't go in mixed glass cullet

If you've ever seen a clean cullet load — graded float glass, ready for re-melt — you'll understand why a sealed unit is a problem. Cullet processors and glass manufacturers buy on contamination tolerances measured in parts per million. An aluminium spacer in a load of cullet is enough to spoil a furnace charge: it doesn't melt at glass temperatures, it stays as inclusions in the new product, and the manufacturer rejects the batch.

The contaminants in an unprocessed IGU are:

• Aluminium or polymer spacer bar
• Butyl primary seal (sticky, smears across glass)
• Polysulphide/polyurethane secondary seal
• Desiccant beads (silica/zeolite — wrong chemistry)
• Setting blocks if they're still attached

Even one whole sealed unit in a 20-yard skip of float drops the cullet grade. That's why our glass service handles intact float and sealed units in different containers, and why a recycler who knows what they're doing will always quote separately for the two streams.

Step-by-step: what happens to your IGU on site, in transit, at the facility

The journey from your van to UK reprocessing runs roughly like this.

1. Frame separation (if the unit's still in the frame)

If you've collected a full window — frame and IGU together — the first job at our facility is deglazing. Beads come off, the unit lifts out, the uPVC frame routes to our profile recycling line, the IGU goes to the glass line. Hardware (hinges, locks, friction stays, steel reinforcement) is separated for metals recycling. You don't need to deglaze before collection — we handle that.

2. IGU handling and staging

Sealed units stage flat, on edge, in stillages. Triple-glazed units are heavier than they look (a 1500 x 1200 triple in 4-12-4-12-4 spec with argon is around 60kg) and they snap easily on the corners — that's where the spacer concentrates the load.

3. Spacer bar separation

This is the step that distinguishes a glass recycler from a skip company. The spacer has to come out. There are two practical methods:

• Manual cutting. A blade run around the perimeter, cutting the secondary seal, prising the panes apart. Slow but works on every spec.
• Mechanical splitters. Purpose-built kit for higher volumes — cut, separate, eject the spacer in one motion.

Once the panes are split, any trapped argon or krypton vents to atmosphere. There's no hazardous-gas issue here — both are inert noble gases, the same chemistry as the air around you, just at a different concentration.

4. Pane cleaning and grading

The panes still have residual butyl on the edge bead. That's scraped, washed or abraded off depending on volume and downstream destination. Glass is graded by type — plain float separated from Low-E (the soft coat affects re-melt chemistry), toughened separated from annealed (toughened can't go back to float manufacture, the heat-treatment changes the surface).

5. Routing to reprocessors

Clean float cullet generally has three onward routes in the UK:

• Container glass and flat glass re-melt. Highest-value end-use, back into new glazing manufacture. Tight contamination specs.
• Glass fibre / mineral wool. More forgiving on contamination, takes mixed-grade cullet.
• Construction aggregate. Lowest-value, but legitimate recovery — used as a sand replacement in concrete and as drainage media.

The Glass and Glazing Federation (GGF) and the wider container/flat glass industry publish cullet quality specs that govern what's acceptable in each route. We grade to the route, not the other way round.

6. Spacer, desiccant, seal — where they go

Aluminium spacer goes to metals recycling — uncontroversial, well-established route, good rebate. Warm-edge polymer spacers route to plastics recycling where the polymer is recoverable, or energy-from-waste where it isn't. Desiccant beads are inert and go to general waste streams. Cured edge seal is mixed polymer waste — energy-from-waste in most cases.

Argon, krypton, triple-glazing — does it change anything?

Short answer: no, not on collection or handling. A triple-glazed argon-filled unit is processed the same way as a single-pane sample of float — the cavity gas vents, the panes separate, the spacers come out. The only practical differences are weight (triples are heavier) and the number of spacers per unit (two, not one).

Krypton is rarer in residential UK stock — you'll see it more in slim-cavity heritage units where the cavity depth is too narrow for argon to perform. Same handling.

What we don't accept without prior arrangement

Our standard sealed unit collection covers double and triple-glazed residential and commercial IGUs in float or Low-E. The following need a phone call first because they need different routing:

• Toughened glass in volume. Can't go back to float manufacture — separate stream.
• Laminated glass with PVB or EVA interlayers. Different processing — the interlayer has to be separated. We can take it but quote separately.
• Shopfront security glass, especially anti-bandit and bullet-resistant grades. Mixed laminate construction.
• Automotive glass. Different chemistry, different supply chain.
• Container glass (bottles, jars). Different industry stream entirely — we don't handle it.
• Wired glass. Old fire-rated stock with embedded steel mesh.

None of this is us being awkward — it's that each of these needs to go to a different reprocessor, and mixing them spoils the standard load. Tell us upfront and we'll route it correctly.

The compliance bit (that nobody enjoys, but matters)

Sealed units are non-hazardous waste under the standard EWC codes (17 02 02 for glass from construction and demolition). They're not special waste, they're not hazardous, but they are waste — which means Section 34 of the Environmental Protection Act 1990 still applies, and you still need a duty-of-care chain from your site to the final reprocessor.

Practically, that means:

• Whoever moves the units must be a registered waste carrier with the Environment Agency. Ours is registration CBDU347776.
• You need a Waste Transfer Note for every collection. We issue eWTNs within 24 hours.
• You should keep the paperwork for two years (general waste) and have it available if DEFRA or the EA come asking.

Same standard that applies to uPVC frame collection — the documentation chain is what separates a recycler from someone with a tipper truck.

Industry context: BPF Recovinyl, GGF, and the closed loop

If you've been in the trade a while, you'll know the British Plastics Federation runs the Recovinyl programme — the European-wide initiative that tracks and verifies post-consumer PVC recovery. That's the framework underneath our closed-loop uPVC story. For glass, the equivalent industry voice is the Glass and Glazing Federation (GGF), which sets the technical standards on glazing performance, cullet quality and end-of-life handling.

The closed loop on glass is real but partial: float cullet does go back into new glazing manufacture, but only the cleanest grades, and only in defined proportions of furnace charge. The rest of UK cullet legitimately ends up in glass fibre and aggregate — both still recovery, both still better than landfill, but not "back into windows" in the way the marketing copy sometimes suggests. We'd rather tell you that straight than oversell it.

Booking a sealed unit collection

For a fabricator or installer with regular IGU waste, the cleanest setup is a dedicated stillage or container on your site, emptied to a schedule that fits your shift pattern. For one-off jobs — a glazier with a van load, an installer clearing a warranty backlog — call or email photos, and we'll book a collection from your nearest of our five hubs.

Five hubs: Chester, Wigan, Haslingden, Stoke-on-Trent and Rotherham. Same or next-day across the North West, Midlands and Yorkshire; same-week elsewhere. Phone 0330 043 5543, or email info@upvcrecycling.com.