# Why PU sealant costs more than silicone per cartridge

> The cost difference is real but it is not where buyers think: raw material, coverage, rework and the hidden cost of a bead that has to be painted twice.

Updated: 2026-11-10 · Source: https://karmindadhesive.com/resources/why-pu-sealant-costs-more-than-silicone/

A PU cartridge usually costs more than a silicone cartridge of the same volume. Buyers notice the invoice line and miss the three lines below it.

## The raw material is genuinely more expensive

Polyurethane prepolymers, isocyanates and the plasticisers and fillers that go into a structural grade cost more than the siloxane chemistry in a general-purpose silicone. That is the visible part of the difference, and it is the smallest part.

## Coverage per cartridge is not the same

Coverage depends on density and on how much of the bead you can actually use. A 310 ml cartridge of PU at density 1.45 g/cm³ delivers roughly 450 g of sealant. The same volume of a filled silicone may be denser or lighter depending on filler load.

The practical number is metres per cartridge at your bead size — and that number moves with the joint, not with the price tag.

## The rework line

This is where PU usually wins the calculation:

- A silicone bead in a body shop contaminates the paint line. One fish-eye repair can cost more than a pallet of cartridges.
- A sealer that is not sandable adds labour at every seam.
- A bead that cracks at 18 months means a warranty visit, and warranty visits are priced in hours, not in grams.

## Where silicone is the cheaper answer

Exposed glazing joints, sanitary work, and any joint that will never be painted and moves a lot. Paying for PU strength in a bathroom is paying for performance nobody uses.

## A way to compare quotes

Ask for cost per linear metre at your bead geometry, not price per cartridge:

```
cost per metre = cartridge price / metres per cartridge
metres = usable volume / bead cross-section area
```

A triangular bead 10 mm wide and 10 mm high has a cross-section of 50 mm². A 310 ml cartridge, allowing 5% waste, gives about 5.9 m. At that point the comparison is between two numbers that mean the same thing.

## The comparison, with numbers

Take a 20 mm × 10 mm joint, 1,000 m of it, and two products at realistic cartridge prices.

```
bead section            20 × 10 ÷ 2 = 100 mm²  → 100 ml/m
PU,   310 ml at USD 6   usable 295 ml → 2.95 m per cartridge → USD 2.03/m
silicone, 310 ml at USD 4  usable 295 ml → 2.95 m → USD 1.36/m
difference              USD 0.67/m → USD 670 over 1,000 m
```

Now the rework side. One paint defect caused by silicone contamination costs a panel preparation and a repaint — hundreds of dollars, and a day of booth time. Three such incidents over the life of the project exceed the entire PU premium.

That is the break-even: the PU premium is recovered if the silicone route causes roughly three paint reworks per 1,000 m. In a body shop or a painted façade, that threshold is met quickly; on an unpainted sanitary joint, it is never met, and silicone is simply cheaper.

## Where the comparison is usually made dishonestly

Suppliers compare cartridge prices, or cost per litre, and stop. Both ignore:

- **Coverage**, which depends on bead section and waste, not on cartridge volume.
- **Process steps**, which differ by chemistry — primer, topcoat, cure window.
- **Rework risk**, which is a probability multiplied by a cost that is much larger than the material.

The only fair number is cost per finished, accepted metre. Everything else is a price, not a cost.

## What this means for buyers

1. Compare cost per metre at your bead size, never price per cartridge.
2. Count the rework risk: paint contamination and sanding labour belong in the comparison.
3. Do not over-specify: silicone is correct for joints that will never be painted.
4. If a quote is far below the market, ask which grade of raw material changed.