BPO Hardener

5 star rating

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  • Item
  • Description
  • Price
  • Qty
  • 266-A
  • 266-A
    Black BPO, 1 oz Tube
  • $5.95
  • 266-B
  • 266-B
    Black BPO, 4 oz Tube
  • $11.95


Easy-Blend Cream Hardener

BPO (benzoyl peroxide) is a peroxide used for curing amine accelerated polyester resins and fillers. It leads to rapid hardening and de-molding, even at low temperatures. It is used with our #4100 and our #4116 fairing and filling compounds. Each kit ships with black hardener.

BPO is sold separately.

  • Available in 2 sizes - 1 oz. and 4 oz.

BPO (Benzoyl Peroxide) is a commonly used catalyst for curing resins, particularly in the context of polyester and vinyl ester resins. Here is some information about the use of BPO as a curing agent:

  1. Curing Process: BPO acts as a free radical initiator that initiates the curing reaction in resin systems. When BPO is added to the resin, it decomposes under heat, releasing free radicals. These free radicals then initiate the crosslinking reaction, causing the resin to harden and cure into a solid composite material.
  2. Mixing with Resin: BPO is typically mixed with the resin just before application. The specific amount of BPO to be added depends on factors such as the resin system, desired curing characteristics, and processing conditions. The resin guidelines and recommendations should be followed for the appropriate BPO-to-resin ratio.
  3. Temperature and Time: The curing process with BPO is usually accelerated by the application of heat. Elevated temperatures help to speed up the decomposition of BPO and the subsequent curing reaction. The temperature and time required for curing depend on the resin system and the desired properties of the final composite.
  4. Safety Precautions: BPO is a hazardous substance and should be handled with caution. It is a strong oxidizing agent and can be flammable. Appropriate safety measures, such as wearing protective gloves, goggles, and working in a well-ventilated area, should be followed. Always consult the safety data sheet (SDS) and follow the manufacturer's guidelines for proper handling, storage, and disposal.
  5. Shelf Life: BPO has a limited shelf life and can degrade over time, which can affect its effectiveness as a curing agent. It is important to check the expiration date and use fresh BPO to ensure reliable curing performance.

It is important to carefully follow the resin guidelines and recommendations for the proper use and handling of BPO or any other curing agent. The specific curing parameters and processing conditions may vary based on the resin system and application requirements.

The choice between white and black BPO (Benzoyl Peroxide) is primarily based on the specific requirements of the application and the desired appearance of the final product. Here are some factors to consider:

  1. Pigmentation: White BPO is typically used when a light-colored or translucent final product is desired. Since BPO can have a slight coloration, using white BPO helps minimize any potential discoloration or tinting of the resin. This is particularly important when working with light-colored or transparent resin systems.
  2. Aesthetics: White BPO is often preferred for applications where the appearance of the cured resin is critical. It helps maintain the intended color and clarity of the resin, ensuring a visually appealing final product.
  3. Visibility: Black BPO, on the other hand, is commonly used when working with dark-colored or opaque resin systems. The black color of the BPO helps blend with the dark resin, reducing any noticeable color differences in the cured composite.
  4. UV Stability: White BPO tends to offer better UV stability compared to black BPO. This can be advantageous in applications where exposure to sunlight or outdoor conditions is expected. The improved UV stability helps prevent yellowing or degradation of the cured composite over time.

It is important to note that the choice of white or black BPO should align with the resin system and the intended visual appearance of the final product. Always refer to the resin guidelines and recommendations for the most suitable catalyst, including the preferred color, to achieve the desired curing and aesthetic properties.


BPO Hardener 1 oz. (#266-A) and 4 oz. (#266-B) units can be shipped via standard ground service without hazard charges within the 48 contiguous United States. All sizes of #266 (1 oz. and 4 oz.) will be subject to a hazard charge if shipped by air. Please see our Hazardous Shipping Chart for more information about hazard fees. We will consolidate items whenever possible to minimize these fees.


BPO Hardener BPO Hardener is available in two sizes that include: One 1 oz. tube of black (#266-A) One 4 oz. tube of black (#266-B)


5 star rating

Product if fine; tube could be more durable

Nov 1, 2021  |  By Jim G

I've used this for a few years and like using the black BPO hardener because it turns the white filler light grey when the two are mixed, which helps you make sure the two parts are properly mixed. I use it any time I don't care if the mixture is not white (which is almost always - the light grey is no problem under white gel coat, e.g.), then if I must have a white mixture I can use white BPO and all the mixing practice I've had makes me confident I've mixed as well as possible.

Most of the time I wish the mixture wouldn't set up quite so fast, so it would be easier to use on larger areas, but that just seems to be the nature of the product, no matter what company makes it.

The thing I really dislike about this is that the tube seems to fail way before using all the hardener. You have to knead the tube before using the BPO because it separates between uses. While kneading I had a tube fail at the point where the body of the tube turns toward the threaded opening, and I had a tube fail at the crimp. Each time I ended up with black fingers and the rest of the hardener in the tube was wasted. In fact, that's why I bought the tube that led to this review; the tube failed at the crimp.


Jan 28, 2021  |  By THOMAS WATSON

Great service and product shipped out the next day!

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