REASONS TO BUY
Solid price for its performance
Stand-out durability
User-friendly visor
REASONS TO AVOID
Runs very hot
Exceptionally heavy
Troy Lee Designs D4 Polyacrylite Review
If you're logging long seasons in the bike park and need something less pricey than the competition, this helmet's worth a look
Credit: Zach Lovell
By Zach Lovell ⋅ Review Editor ⋅ October 8, 2025
Our Verdict
The Troy Lee Designs D4 Polyacrylite is a gravity-oriented design meant for bike parks and shuttle laps with limited pedaling. In this sub-class of full face helmets, many models are very expensive, especially when compared to enduro/lighter duty designs. Still, the D4 is as much as half the price of the gravity-fed competition. Outside of its price point, this helmet stood out for its impact test results, which were among the best in the entire review. While we wouldn't recommend pedaling or pushing a bike uphill for long periods of time in the D4, it vents well enough for lift or shuttle riding. As is common with a helmet designed for more aggressive downhill, this model is quite heavy, though we found it exceptionally durable.
Our Analysis and Test Results
We thoroughly enjoyed bike park laps in the Troy Lee Designs D4, from flow tracks to jump lines. Our pedaling tests were less pleasant, but showcased how important proper ventilation is on warm days. In this sub-class of full face helmets, the D4 is a bargain and shouldn't be missed as you research various models for gravity-only bike rides.
At first, it might not look like a deal, but the D4 is a great budget model for its class of full face helmet.
Credit: Zach Lovell
Impact Test
The TLD D4 performed remarkably well in our impact testing, posting impressive data in both slow and fast impact tests. The helmet carries an EU2016/425, and EN 1078:2012+A1 2012 certifications that ensure it's safe. Our impact testing examines how each helmet responds to slow and fast impacts in a lab using sensitive equipment that helps us compare their performance.
The D4 tied for second place in our slow impact test, with data that outshone most of the other helmets. In fast impact testing, the sensors in the helmet showed that this helmet performed better than all others, except for the $550 Poc Coron Air. While this helmet's weight and airflow feel less impressive, they may be worthwhile trade-offs for such impressive impact scores. The D4 uses a MIPS C2 liner for rotational impact protection.
The D4 boasts excellent performance in its drop testing.
Comfort
We found the D4 Polyacrylite to be generally comfy to wear, though it took a bit longer to break in the padding. As a model designed for lengthy days riding chair lifts and ripping jarring descents, we appreciated its snug fit on bumpy trails.
As is common with this class of helmet, the D4 does not have an adjustable retention system, so breaking in the pads or adjusting the pad sizing are your only means to adjusting the fit. Fortunately, Troy Lee Designs did an excellent job designing the layout around the ears, not over, and none of our testers complained of any unnecessary ear or jaw pressure.
We greatly appreciated the cushioning of the D4, especially considering its intended uses in a bike park or shuttle lap.
Credit: Zach Lovell
Ventilation
While the D4 has multiple vents, it isn't a particularly breathable helmet. As a downhill helmet, it prioritizes safety over airflow. The substantial padding and snug fit reduce the cooling effect you can get from the limited amount of airflow.
We weren't surprised that the D4 fell back in the pack, with a heavier construction than most of the helmets we tested. Even for short pedals, our team definitely got sweaty, and if sessioning a feature, pushing our bikes uphill was less enjoyable. Keep in mind that this is a model that's designed for downhill all day, and in this subclass of full face helmet, the D4's performance is par for the course.
We had a tough time examining the ventilation of the D4, but we're happy to do it in the name of comprehensive testing.
Credit: Zach Lovell
Usability
Easy-to-swap pads and a no-frills helmet bag are in the asset list. We appreciated how easy it was to adjust the visor, which still breaks away in the event of a crash. The shell is less flexible, making it harder to get over the ears, and the chinstrap was a bit of a chore, but the D4 felt particularly durable, and we didn't worry about times when it rolled around in the back of our shuttle van.
The polyacrylite construction used in the D4 shell is gaining popularity in the full face helmet market. It's a durable and relatively inexpensive material to use, and when paired with an EPS liner, and offers a high level of protection. The D4 line from Troy Lee Designs is available in both carbon and composite (polyacrylite) construction materials, but the former significantly increases the cost, so we recommend sticking with the polyacrylite if cost is a priority.
In addition to its durability, we appreciated the visor's adjustability.
Credit: Zach Lovell
Weight
At 41.8 ounces, the D4 Polyacrylite is quite heavy. It weighs substantially more than some of the enduro helmets in the review, with some weighing more than a pound less, is this the cost of safety?
When considering its durability, the weight of the D4 might not be a deal breaker, especially as a downhill-only helmet. No one is going to stop you from pedaling uphill in this thing, but it is first and foremost designed to be a gravity-fed biking helmet, in a world where riders are strapping on mass-tuned dampers and weights on the bottom bracket, a few more ounces on your helmet isn't a big deal.
The D4 is among the heaviest helmets we've tested, though it's got impressive durability.
Credit: Zach Lovell
Should You Buy the Troy Lee Designs D4 Polyacrylite?
If you're a bike park season pass holder or log a bunch of days shuttling cars, you might be looking for a more downhill-only type helmet that favors protection and durability over ventilation. In that world, costs can be astronomical, but the Troy Lee Designs D4 Polyacrylite can ease the pain of your wallet if you can't stomach the high price tag. If you're looking for something that can handle enduro pedals, we'd look elsewhere, but if gravity is your game, the D4 is worth your consideration.
What Other Full Face Helmets Should You Consider?
Check out the top-scoring POC Coron Air Carbon Mips if you're not price-sensitive and demand the best in downhill helmets. If you're needing something more breathable, consider the Specialized Gambit, which is one of the lightest full-face helmets we've tested yet.
Side-by-Side Comparison
Compare Troy Lee Designs D4 Polyacrylite versus top competing products:
—Zach Lovell
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