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One K (#21807)

One K Defender Matte Helmet

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Your Price:
(You save 5% as a member of . Because you have supplements on AutoShip, you can save an extra 10% on this and all other SmartPak tack & apparel items! Enter promo code PERKS at checkout.)
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As riders and online shoppers, we know it can be tough to buy a new bridle or pair of boots without trying them on. That's why we moved the fitting room to your living room (or barn)! From breeches to blankets, if you or your horse can try it on, you can return it, free! Just request a return with a FREE SmartPak return label from your Order History within 60 days of the purchase date. And of course, please make sure the item is in like-new condition with original packaging (we said 'fitting room', not 'war room'!).

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FINAL SALE - This item cannot be returned or exchanged.

FINAL SALE - This item cannot be returned or exchanged.

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You'll love our AutoShip because it's:
  • Focused on happy riders - never worry about running out!
  • Easy to snooze or cancel online, anytime
  • Totally flexible - edit your order as often as you'd like
PLUS! You'll save % on every shipment if you order this product on AutoShip
You'll love our AutoShip because it's:
  • Focused on healthy s, because consistency is key
  • Easy to snooze or cancel online, anytime
  • Totally flexible - edit your order as often as you'd like
  • Your VIP pass to FREE SmartPerks benefits
PLUS! You'll save % on every shipment if you order this product on AutoShip
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Start date: Customize your program for estimated start date. View estimated schedule
Zone Map
Begin with the zone for the state you are in. Dates shown on the map indicate suggested start and end dates for Fly Stoppers™ shipments. You may want to shift a zone if your elevation or microclimate is unusual, or if you fall on the border between two zones. You can start anytime during the fly season. Choose "Year Round" for climates that have flies all year, and start now.
Program Type Shipment/Application Frequency
Regular Programs: Ships every 4 weeks. For low to average fly levels, frequent manure management and few neighbors.
Premium Programs: Ships every 3 weeks. For high fly levels or weekly manure management or nearby livestock.
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Before purchasing this item, please note:

  1. This item can't be shipped to a PO Box.
  2. This product will be shipped directly from the manufacturer using a shipping company.
  3. The freight company will call you to schedule a delivery appointment.
  4. If SmartPak and the shipper are unable to contact you within 7 business days of the product shipping out, your order will be cancelled.
  5. You may be liable for any storage fees due to missed delivery appointments or requests for dates beyond the standard delivery window.
  6. When your shipment arrives, you will be responsible for inspecting the shipment to make sure it's complete and that no items are damaged.
  7. Before accepting the shipment and signing for it, you must record missing items and damaged items on the receipt, and take pictures of any damage.
  8. SmartPak and the manufacturer will not be able to assist you in filing a claim if you haven't noted any damage on the receipt. You will be responsible for filing any claims.

Shipping is not available to Alaska or Hawaii for this item. We apologize for any inconvenience.
Unfortunately, we cannot guarantee that customization items will be delivered by Christmas. If you're adding customization to this item, please note the estimated arrival date in your cart.
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All customized items are personalized in our Plymouth, MA facility, and it looks like this item is currently out of stock in that location.
Please call 1-800-461-8898 to order this product.
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We're bringing you this product at the lowest price allowed by the manufacturer so you won't find it cheaper anywhere else. This also means we can't apply any further discounts or promotions.
We're sorry this item is currently out of stock. Our team is working to get it back in stock asap.

SmartPerks Putting your horse's supplements on AutoShip helps you take great care of your horse, so we take great care of you with SmartPerks! When you order your horse's supplements on AutoShip, you're automatically* eligible for our FREE SmartPerks benefits, including:

  • Free shipping every day
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*At least one individual AutoShip supplement or horse's SmartPaks must be over $40. Some exclusions apply. Visit or call 1-800-461-8898 for details.


Why We Love This

One K™ Defender riding helmets boast the perfect synergy between advanced technology and aesthetically pleasing design. This helmet features a polycarbonate and advanced ABS composite outer shell that’s tough but lightweight with a modern matte finish. It’s offered in both an oval shape and a round shape so that you can find the perfect fit for your head. You’ll love that the liner is moisture wicking, quick drying, anti-microbial, and washable to keep you cool, dry, and comfortable. Plus, the harness is padded for comfort and lined with easy-to-care-for synthetic suede to keep you as comfortable as you are stylish. It even has a Fastex buckle that makes taking it quick and easy to take on and off. Additionally, you’ll have plenty of ventilation with two side, two front, one back, and two center stripe vents for a total of seven vents. Last but not least, this helmet is ASTM/SEI F1163-15 certified, so you can have peace of mind that your head is in good heads. With enough features to appeal to those seeking everything a horseback riding helmet could offer, wrapped in a stylish package that traditionalists can appreciate, One K™ has the best of both worlds.

Additional One K Helmet Liners also available!


CAUTION: Safety equipment must fit properly and be appropriately secured with manufacture approved parts only. Altering or adding to safety equipment voids warranty and can result in injury. As a safety precaution, inspect all products prior to each use.

For additional information on fit, watch our video on how to fit your helmet. Click Here!

  • Polycarbonate and advanced ABS composite outer shell is tough but lightweight
  • Offered in oval and round shapes for a great fit
  • Inner lining is anti-microbial, moisture wicking, quick drying, and washable
  • Comfort padded harness with synthetic suede lining and Fastex buckle is comfortable, easy to use, and stylish
  • ASTM/SEI F1163-15 certified
  • Lots of vents to keep you cool and dry
  • Stylish design looks great in the ring
Key Specifications
  • ASTM/SEI: Yes
  • Oval: Yes
  • Round : Yes
(Maintenance Dose = )
Ingredient Amount
What Customers Say:
Sizing Chart for One K Defender Matte Helmet
Oval Yes
Round Yes
One K Defender Matte Helmet is rated 4.8 out of 5 by 192.
Rated 5 out of 5 by from My Second One Love these helmets! Finally a great helmet for us petite people! I have the black suede style for foxhunting and the brown plastic for exercising since it matches my gear. I usually wear about a 7 in most helmets including all of my GPAs(RIP First Lady) and the same with this one, medium oval is perfect. I just can justify their price anymore so these are great! ***Pro Tip*** I saw some people comment on the strap Velcro part, I just bought double sided Velcro and wrapped out around it. You could also just cut a strip to lay on it as well.
Date published: 2023-02-10
Rated 5 out of 5 by from Better than expected This helmet has more features than I expected. It fits perfectly and I just love it!
Date published: 2022-09-23
Rated 5 out of 5 by from My favorite helmet! This is my second One K Defender helmet. I love the way it fits, looks and it keeps my heads very cool which is super important to me!!! I wanted the wide brim, but they don’t have the side vents, which is very disappointing! I did have to order up a size from my first One K helmet. Not sure why this new one seemed to fit tighter? All in all, it is a GREAT helmet!!
Date published: 2022-07-09
Rated 5 out of 5 by from Good fit and comfort Finally bought an oval helmet, and what a difference. I've gone through many helmets, and this is my all time favorite. I love the snug fit without being too tight. Chin strap fits comfortably, and the helmet looks good too.
Date published: 2022-03-02
Rated 5 out of 5 by from Comfortable helmet that fits great Love the removable inner liner! Highly recommended. Excellent helmet at a great price!
Date published: 2021-10-22
Rated 5 out of 5 by from So comfortable This is the best fitting helmet I’ve ever owned, plus it is very comfortable in hot weather
Date published: 2021-08-12
Rated 4 out of 5 by from AMAZING HELMET!! Disappointing chin strap. This helmet is amaaaazing. It feels as supportive as high waisted, stretchy jeans on a bloated day…but for your head lol. The liner has a memory foam feeling which is nice because my M-round is still getting molded to my head shape (perfect fit, not too tight) so I don’t have to worry about headaches. BUT THE CHIN STRAP. If you lengthen it too much, you’re not able to Velcro it (see pic). I guess I will just rock the double chin? Anyways, this helmet is pure gold. Get it! But just ignore the chin strap entirely.
Date published: 2021-07-09
Rated 5 out of 5 by from My favorite helmet! The most comfortable helmet I've owned. I love it so much I got it in all colors. It fits my head perfectly, and especially love the fact that I can choose between long oval and round fit! The long oval has been the best thing yet for my head shape. No more front head pressure points! The matte material is so easy to clean with a damp cloth, and I can take the padding out and wash it too. This helmet is perfect for every use no matter if you want to use it for schooling, clinics, or shows. I personally always have two of the same to keep one nice for the show.
Date published: 2021-04-19
Rated 5 out of 5 by from Sleek style and great quality! I had to get a new helmet after falling in my old one and hitting my head pretty hard. I know a bunch of my riding friends have this brand of helmet so I decided to try it out and I love it more than my old one! It fits really well and looks so nice when I’m wearing it!
Date published: 2021-03-03
Rated 5 out of 5 by from Perfect fit I was due to purchase a new helmet and decided to get this one. I wore it last night during my hack and it fit perfectly and was comfortable throughout my whole ride. I also love how easy and convenient the adjustment for the chin strap is, and how easy to clean the helmet is.
Date published: 2021-03-03
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Q & A
One K Defender Matte Helmet Review
Katie from SmartPak talks about why she thinks the One K Defender Matte Helmet ( is so smart. The smartest reason to get yours at SmartPak? Free Shipping Both Ways! At, you’ll get free shipping every day on all orders over $75 and free returns on all sized items. Just another way it pays to be $mart.
How to Shop for a Helmet
Have you ever struggled with the idea of buying a helmet online? Watch this video for tips & tricks on getting the right helmet fit.

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