Serious Steel Fitness' Gym Backpack is 45 litres of 1000D nylon at $129.90, with an integrated lifting-belt holding system, a mesh-ventilated shoe compartment, an internal garment bag and a 14" padded laptop pocket. It fits TSA carry-on dimensions at 21" × 12.5" × 8". At the time of writing it is on backorder.
This is the most travel-oriented pack in the 45L gym class, and it is the only one that fits standard carry-on dimensions. That single fact will decide it for some people.
It is also the most expensive of the mainstream 45L options at $129.90, has the smallest published laptop capacity of any pack that publishes one, and is currently out of stock.
Where Serious Steel is genuinely strong
1000D nylon. Heavier yarn than the 900D used by IronBackpack, TuffWraps, HolStrength and Built for Athletes. Denier is not the whole durability story — weave and coating matter too — but it is a real spec advantage and worth paying for if abrasion resistance is your priority.
TSA carry-on approved at 21" × 12.5" × 8". This is the differentiator. The common US domestic carry-on limit is 22" × 14" × 9", and this pack fits inside it. The IronBackpack Pro 45L at 20" × 12" × 12" exceeds that limit in depth. If you fly to competitions with one bag, that matters more than anything else on the spec sheet.
Integrated belt holding system. External loops let you wrap a lifting belt around the outside of the pack rather than folding it inside. A designed solution to a real problem.
Mesh-ventilated shoe compartment. Bottom-loading with ventilated siding to move odour out. Better executed than most.
Internal garment bag on Velcro. A removable pouch that doubles as a toiletries bag. From a verified 5-star buyer:
"It has molle webbing on the outside and INSIDE, to attach small bags or other attachements... It also has this interior bag that attaches with velcro on the inside that i fold and use as a toiletries bag for travelling."
What to weigh before buying
The 14" laptop pocket. Serious Steel publishes "fits up to 14" laptop" with three padded layers and a safety strap. That is well-built but small. Of the packs that publish a laptop size, this is the lowest.
Backordered. At the time of writing the product page states the bag is on backorder and will ship when back in stock.
One colourway. Black only.
A 1-star review worth reading. Not every review is glowing, and the criticism is specific:
"Once the belt is wrapped around the bag, it's a struggle to put anything inside. On the flip side, if I place my items in first, getting the belt around is equally frustrating. The bag is also awkwardly tall for a 45L size. I wish it were wider instead of taller."
Overall the pack sits at 4.69 stars from 13 reviews, with 92% at five stars. The complaint above is one voice, but it points at a real design trade-off: the belt system and the packing order interact.
Side-by-side
| Spec | Serious Steel Fitness 45L | IronBackpack Pro 45L |
|---|---|---|
| Price | $129.90 | $99.95 |
| Cost per litre | $2.89 | $2.22 |
| Volume | 45 L | 45 L |
| Dimensions | 21" × 12.5" × 8" | 20" × 12" × 12" |
| TSA carry-on size | Yes | No — exceeds depth |
| Material | 1000D nylon | 900D high-density polyester, water-resistant |
| Laptop | 14" padded, 3 layers | 17" padded sleeve |
| Shoe compartment | Yes, mesh ventilated | Yes, 1 of 5 separated compartments |
| Belt carry | Integrated external loops | MOLLE webbing |
| Internal garment bag | Yes, removable | No |
| Opens flat 180° | Not published | Yes |
| Load rating | Not published | 20 kg / 44 lb |
| Warranty | Not published | Limited lifetime |
| Free shipping | Orders over $99 | Every order, no minimum |
| Colourways | 1 | 3 |
| Availability | Backordered | In stock |
| Reviews | 4.69 ★ from 13 | See product page |
Specs, prices and stock from each brand's own site, checked 16 August 2026. Verify current listings before buying.
Which one fits you
Buy the Serious Steel Fitness 45L if you fly to competitions and want one bag that goes in the overhead bin, if 1000D nylon over 900D is worth $30 to you, or if the integrated belt loops and removable garment bag solve problems you actually have. Accept the 14" laptop limit and the wait for stock.
Buy the IronBackpack Pro 45L if you carry a 15" or larger laptop, if you want the bag now, or if $99.95 with a published limited lifetime warranty and free shipping on every order fits your priorities better than carry-on dimensions.
The clean split: flying with it → Serious Steel. Working out of it → IronBackpack.
See the IronBackpack Pro 45L — $99.95, in stock, free shipping →
More: full 45L comparison · TUFF Pro 45L · WOLFpak 45L
FAQ
How much is the Serious Steel Fitness backpack?
Serious Steel Fitness lists the 45L Gym Backpack at $129.90. Free shipping applies on contiguous US orders over $99. At the time of writing the product is on backorder and ships when stock returns. Prices and availability change — check the current listing.
Is the Serious Steel backpack carry-on approved?
Serious Steel states the 45L is carry-on approved at 21" × 12.5" × 8", within the common US domestic limit of 22" × 14" × 9". It is the only 45L pack in this comparison that fits those dimensions. Airline allowances vary, so confirm with your carrier before travelling.
What size laptop fits in the Serious Steel backpack?
Serious Steel publishes a padded laptop pocket fitting up to 14 inches, with three padded layers and a heavy-duty safety strap on the back panel. A 16-inch laptop will not fit. By comparison, the IronBackpack Pro 45L and Built for Athletes Hero 45L both publish a 17-inch capacity.
Is 1000D nylon better than 900D polyester?
Denier measures yarn thickness, so 1000D generally means a thicker, more abrasion-resistant yarn than 900D. Weave density, coating and stitching also affect real-world durability, so denier alone does not settle it. Serious Steel uses 1000D nylon; IronBackpack, TuffWraps, HolStrength and Built for Athletes use 900D.
Does the Serious Steel backpack hold a lifting belt?
Yes. Serious Steel includes an integrated belt holding system — external loops that let you wrap a lifting belt around the outside of the pack rather than folding it inside. One verified reviewer noted that with the belt fitted, loading the main compartment becomes harder, so packing order matters.
What is a good alternative to the Serious Steel Fitness backpack?
The IronBackpack Pro 45L offers the same 45-litre capacity with a 17" laptop sleeve, five separated compartments, a 180° clamshell and MOLLE webbing at $99.95, in stock, with free shipping on every order and a limited lifetime warranty. It does not fit carry-on dimensions, at 20" × 12" × 12".
Flying with it? Serious Steel. Working out of it? This one.
Shop IronBackpack Pro 45L — $99.95 · See all backpacks
