Choosing Windshield Repair Resin by Damage Type

Star break, use LV. Bullseye or combination break, use HV in hot weather and MV otherwise. Long crack, use CR. Cap the pit with PF or PFAF. Those four choices cover most of this type of work. Two things to make sure to consider: temperature, which overrides the break type entirely, and the half-inch rule on HV, which GT Tools states as a prohibition rather than a preference. This guide covers all six DiamondClear resins, what each is formulated for, the temperature rules, and the tint and bottle-size choices available.

Match the Resin to the Break

Four repair resins and two pit fillers cover almost any damage a technician sees.

Damage	Resin	Why
Star break	DiamondClear LV	Low viscosity travels down thin legs
Bullseye	DiamondClear HV in heat, MV otherwise	Thicker resin suits an open cavity
Combination break	HV in heat, MV otherwise	Both a cavity and legs to fill
Short crack	MV	Balanced flow into a narrow opening
Long crack	DiamondClear CR	Tensile strength and holding power along the run
Star with a long crack	CR	Handles the leg and the crack in one pass
Finishing the pit	PFAF, or PF for larger pits	Seals the surface and restores the finish

Formulations checked against the product pages 9 September 2026.

What viscosity changes

Viscosity is how readily the resin moves once the injector pulls vacuum and then pushes pressure. A thin resin travels further into a narrow opening, which is what a star break needs, because the legs of a star taper to nothing and a thicker resin stops partway down. A bullseye is the opposite problem: an open cavity rather than a set of fine channels, which is why the high-viscosity resin is the one specified for bullseyes and combination breaks rather than the thin one.

Temperature shifts the same property without changing the bottle, which is why the guidance below can override the break type entirely.

The four repair resins

LV, low viscosity. Designed for star breaks. It is acrylic acid free with an index match for glass and contains UV inhibitors to prevent yellowing. It has a second use: in cold weather, when lower temperatures slow every repair down, LV works on all break types, not only stars.

MV, medium viscosity. The widest working range of the four. It suits bullseyes, star breaks, combination breaks and short cracks, with balanced flow for penetration into a crack and a refractive index that closely matches automotive glass. If you stock one resin, this is the one that covers the most damage.

CR, medium-to-low viscosity. Built for long cracks. It is acrylic acid free with dynamic holding power and high tensile strength, it has an excellent refractive index, and it works on star breaks that have thrown a long crack.

HV, high viscosity. A hot-weather resin for bullseyes and combination breaks. It also conceals vinyl damage caused by severe impacts. One published restriction applies to it, covered below.

All four are BSI tested, by the British Standards Institution.

Temperature Overrides Break Type

Two of the four resins have published temperature guidance, and it takes precedence over the break-type table above.

Below 60 degrees Fahrenheit, use LV. That applies to every break type, not only stars. Cold thickens resin and slows the fill, and a low-viscosity formula compensates. A warming source on the windshield is still recommended below 60 degrees; LV does not replace it.

Above 85 degrees Fahrenheit, use HV. Heat thins resin, so a bullseye that would take MV in spring probably needs HV in July.

Between those two figures, MV is the working default and you choose by break type.

The half-inch rule on HV

GT Tools publishes one explicit prohibition on the HV page: do not use HV when radial cracks exceed half an inch. Use MV instead.

It is easy to miss, because a combination break with a half-inch leg looks like an HV job right up until the leg is measured. Measure the longest radial before you choose.

Pit Fillers Do a Different Job

The repair resin fills the damage. The pit filler closes the surface. Skipping the second step leaves an open pit that takes in water, dirt and road salt.

PFAF, medium viscosity. The finishing resin for most repairs. It seals the repaired area from rain, snow and sun, and restores the pit to a high luster.

PF, high viscosity. For larger pits, and for filling and capping any star, bullseye or combination break. It has very high tensile strength, which is what seals the repair, prolongs its life and prevents contaminants from entering.

Both are $39.00 for 15cc and $69.00 for 30cc, the same as the repair resins, and both are BSI tested. A technician working from a full kit uses two bottles on a single repair: one repair resin, one pit filler.

The order of operations

The published sequence on the resin pages: clean the damaged area thoroughly, position the applicator over the chip or crack, work the resin into the damage, let it fill every gap, cure with UV light or sunlight, then remove the excess and polish the surface.

The pit filler goes on after the repair resin has filled the break, not alongside it. Cured resin cannot be re-injected, so the fill has to be complete before the lamp comes out. That is the practical argument for matching the resin to the break rather than reaching for whatever bottle is nearest: a thin resin in an open cavity or a thick one in a fine leg is a problem you find out about after the cure, when it is too late to fix.

Long Cracks Need Hardware as Well as Resin

CR is the resin for a long crack, but resin alone does not close one. A long crack has to be held while it fills.

Crack Jacks are $28.40 for a single and $66.20 for a 3-pack. They mount on the interior of the windshield, spaced 3 to 5 inches apart along the crack with the pressure point centered on it, and they are made for the field of the glass rather than the edge.

The Crack Repair System is $132.30 and packages the whole job: three standard Crack Jacks, a 15cc PF, a 15cc CR, pit tape and a needle cap. Three Crack Jacks on their own are $85.20 and the two 15cc resins are $39.00 each, so the parts come to $163.20 before the pit tape and needle cap. The system is compatible with any windshield repair bridge, so it works alongside equipment you already own.

What is repairable in the first place

The published threshold is chips smaller than a quarter, or cracks less than 3 inches, and not in the driver's line of sight. Damage beyond that means replacing the windshield, and no resin choice changes it.

The industry standard covering this is ANSI/AGSC/NWRD ROLAGS 002-2022, the Repair of Laminated Automotive Glass Standard, which sets out damage classification, repairable dimensions and repair limitations. Check its limitations section on a borderline job.

Bottle Size and Tint

Three purchasing details to be aware of.

The 30cc bottle is the cheaper way to buy volume. At $69.00 it is $9.00 less than two 15cc bottles at $39.00 each, for the same 30cc of resin.

The 30cc bottle is Clear only. Tinted resin comes in 15cc. If you want Blue Green, Amber or Gray, you are buying 15cc bottles regardless of volume, and the discount above does not apply.

Tint is optical, not cosmetic. The tinted resins have a cured refractive index that more closely matches tinted glass of that color. On a tinted windshield, clear resin cures to a slightly different index than the glass around it, and the repair reads as a mark from certain angles.

CR has no tint options, so a long crack in tinted glass is repaired with clear resin. That is a limitation to know before quoting the job.

What a full resin shelf looks like

A shop covering everything stocks five bottles: LV, MV, CR, HV and a pit filler. At $39.00 for 15cc that is $195.00 to cover every break type in every season. Volume shops should opt for 30cc, at $69.00, for whichever two they run out of fastest. For most that is the pit filler, which every repair uses, and MV, which covers the most break types. A shop working outdoors through a real winter and a real summer runs out of LV and HV at opposite ends of the year, so those two are worth watching seasonally rather than by volume.

Frequently Asked Questions

Which windshield repair resin should I use for a star break?

DiamondClear LV. Low viscosity travels down the thin legs of a star, which is where a thicker resin stalls and leaves the legs unfilled. LV is $39.00 for 15cc and $69.00 for 30cc, acrylic acid free, with an index match for glass and UV inhibitors that prevent yellowing. If the star has thrown a long crack, use CR instead, which is formulated for that combination.

What is the best resin for a long crack?

DiamondClear CR, a medium-to-low viscosity resin with dynamic holding power and high tensile strength, built for longer cracks and for stars with long cracks. Resin is only half the job on a long crack: Crack Jacks hold the glass while it fills, spaced 3 to 5 inches apart on the interior with the pressure point centered on the crack. The Crack Repair System at $132.30 packages three Crack Jacks with CR, PF, pit tape and a needle cap.

Does temperature change which resin I use?

Yes, and it overrides break type. Below 60 degrees Fahrenheit, use LV on every break type, not only stars, because cold slows the fill. A warming source on the windshield is still recommended at those temperatures. Above 85 degrees, use HV on bullseyes and combination breaks. Between the two, MV is the working default and you choose by damage.

When should I not use HV resin?

When any radial crack exceeds half an inch. The HV product page states this as a prohibition rather than a preference, and directs you to MV instead. The trap is a combination break: it looks like an HV job until you measure the longest leg. Measure before choosing.

What is the difference between PF and PFAF pit filler?

Viscosity and the size of the pit. PFAF is medium viscosity and finishes most repairs, sealing the area from rain, snow and sun and restoring the pit to a high luster. PF is high viscosity, for larger pits and for filling and capping any star, bullseye or combination break, with very high tensile strength that keeps contaminants out. Both are $39.00 for 15cc and $69.00 for 30cc.

Do I need tinted resin?

On tinted glass, yes, if you care how the repair looks. The Blue Green, Amber and Gray resins cure to a refractive index that more closely matches tinted glass of that color, so the repair disappears rather than showing as a mark. Tinted resin is available in 15cc only; the 30cc bottle is Clear. CR has no tinted version, so long-crack repairs in tinted glass use clear resin.

How much damage is too much to repair?

GT Tools publishes the threshold as chips smaller than a quarter, or cracks less than 3 inches, and not in the driver's line of sight. Beyond that the windshield is a replacement rather than a repair. ROLAGS 002-2022, the ANSI standard for laminated auto glass repair, covers damage classification and repairable dimensions in more detail and is the reference to check when a job is near the line.

Compare the full resin range in the Windshield Repair Resins collection, browse 15cc bottles for tinted options, or reach the team at gtglass.com to work out what your shelf should carry.