Fiberglass Bumper Repair Kit: Choosing a Kit (2026)

A cracked fiberglass bumper can be fixed in the garage with a resin kit, and a fiberglass bumper repair kit is the box that holds the resin, hardener and cloth for the job. This guide shows what is in each kit, how the mix and cloth work, and which kit fits your repair.

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Below: what is in a repair kit, how resin, hardener and cloth work together, the steps to a repair that holds, and the kits to pick from.

#	Product	Shop Score	Buy
1	Fiberglass Repair Kit, Anti Sagging Formula	9.6/10	Buy on Amazon
2	Bondo Fiberglass Resin Repair Kit, 00422	9.5/10	Buy on Amazon
3	Bondo Fiberglass Resin Repair Kit, 00420	9.4/10	Buy on Amazon

1

Fiberglass Repair Kit, Anti Sagging Formula

Mshunya·9.6/10 Shop Score

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The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A 200g resin and 100g hardener kit with 300g of fiberglass cloth for structural repairs to cracked bumpers and panels, with an anti-sagging formula for vertical surfaces.

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Pros

• 200g resin plus 100g hardener in a precise 2:1 mixing system
• 300g fiberglass cloth for a smooth, bubble-free laminate
• Anti-sagging formula with no drip or run as it hardens on vertical surfaces
• Kit includes a 60ml measuring cup, 2 stirring sticks, a brush, gloves and 3 sheets of sandpaper

Cons

• Hardening time varies with temperature and humidity, so timing is not fixed
• Resin A may freeze in cold weather and needs thawing in warm water
• Safety goggles are advised on vertical surfaces but are not included
• Only one size is offered, so a small touch-up may need more kit than the job needs

2

Bondo Fiberglass Resin Repair Kit, 00422

3M·9.5/10 Shop Score

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The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A 0.9 quart resin kit with liquid hardener, spreader and fiberglass cloth for repairing holes and scratches on cars and boats, sandable in under 2 hours.

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Pros

• 0.9 quart of resin for larger holes and rebuilds
• Maker states a 100% waterproof seal for long-lasting repairs
• Sandable in under 2 hours
• Kit includes resin, liquid hardener, spreader, cloth, mixing stick and tray

Cons

• No measuring cup is included for the resin and hardener mix
• Heavier at 2.8 pounds than the 0.45 pint kit at 0.8 pounds
• The same formula as the smaller 00420, so a small repair may not need the larger size
• No gloves or goggles are included in the box

3

Bondo Fiberglass Resin Repair Kit, 00420

3M·9.4/10 Shop Score

i

The Shop Score runs from 9.2 to 9.8 and weighs performance (35%), build (25%), value (25%), safety (10%, where it applies) and warranty (5%), using only what the manufacturer and the listing publish. How we pick ›

A 0.45 pint resin kit with the same resin, hardener, spreader and cloth as the larger Bondo kit, for small holes and scratches.

Check price on Amazon

Pros

• 0.45 pint size suits small holes and scratches
• Maker states a 100% waterproof seal for long-lasting repairs
• Sandable in under 2 hours
• Kit includes resin, liquid hardener, spreader, cloth, mixing stick and tray

Cons

• The smaller of the two Bondo sizes, so a large repair needs more than one kit
• No measuring cup is included for the resin and hardener mix
• No gloves or goggles are included in the box
• The same formula as the 0.9 quart kit, so a buyer who needs more resin must buy the larger kit

Fiberglass bumper repair kit: what is in the box

Every kit here holds the same parts: resin, a hardener to mix in, and fiberglass cloth. The Mshunya kit lists exact amounts for each one, while the Bondo kits list the resin size and the tools in the box.

The Mshunya kit is the only one here with a measuring cup, stirring sticks, gloves and sandpaper, and the Bondo kits are the only ones here with a mixing tray and spreader. For cracks and holes in a bumper, see our bumper crack repair kit guide.

How resin, hardener and cloth work together

Resin alone is a liquid; mixed with hardener it hardens into a solid layer, and cloth laid into the mix gives the repair its strength. The Mshunya kit states a precise 2:1 mix of 200g resin to 100g hardener, and its 300g cloth creates a smooth, bubble-free laminate. The maker states structural-level repairs, and the laminate takes paint or varnish directly.

Hardening is not instant. The Mshunya listing states hardening time varies with temperature and humidity, and the Bondo kits state the repair is sandable in under 2 hours. Resin can freeze in cold weather: the Mshunya listing states resin A may freeze and gives thawing in warm water, 10 mins in 60℃ water or 7 mins in 80 to 100℃ water, before use.

How to use a fiberglass bumper repair kit: the steps

1. Mix resin and hardener. The Mshunya kit uses a precise 2:1 mix, measured with the 60ml cup and mixed with the stirring sticks.
2. Lay in the cloth. Press fiberglass cloth into the mix for a smooth laminate.
3. Apply thin coats on vertical surfaces. The Mshunya kit advises multiple thin coats instead of one thick coat, and its anti-sagging formula avoids dripping or running as it hardens.
4. Wear protection. The Mshunya kit includes protective gloves and advises safety goggles when working on vertical surfaces.
5. Let it harden, then sand. The Bondo kits are sandable in under 2 hours.
6. Paint or varnish. The Mshunya laminate allows direct painting or varnish application.

The gear: fiberglass bumper repair kits

Once you know the mix, the cloth and the coats the job needs, pick a kit with enough resin and cloth for the damage, and the kits below cover small scratches through structural repairs.

FAQ: garage tools

Can a fiberglass bumper repair kit fix a crack?

Yes, for cracks in fiberglass. The Mshunya kit states structural-level repairs for cracked car panels, and the Bondo kits state repairs for holes and scratches.

How long before I can sand the repair?

The Bondo kits state sandable in under 2 hours. The Mshunya listing states hardening time varies with temperature and humidity, so follow the manual in the box.

What mix ratio does the Mshunya kit use?

A precise 2:1 mix of 200g resin to 100g hardener, with a 60ml measuring cup and 2 stirring sticks in the box.

Can I use the kit on a vertical bumper surface?

Yes. The Mshunya kit states an anti-sagging formula with no drip or run as it hardens on vertical, overhead and curved surfaces, and advises safety goggles on vertical surfaces.

Does the resin work on surfaces other than fiberglass?

Yes. The Mshunya resin bonds carbon fiber, fiberglass, metal, wood and plastic, and the Bondo formula covers concrete, wood, fiberglass and metal.

Related: our bumper crack repair kit guide, the bumper scratch repair kit guide, our engine and shop equipment hub and the best glazing putty for plastic picks.