This isn’t going to be a scored review because, while other companies might release an internal framed version of their most popular pack as a standalone item, Tom Bihn has decided to make the internal frame an accessory. That alone tells you all you need to know about how about clever and how focused Tom Bihn is on making some of the best gear in the world.

Here is the product page. The Internal Frame costs $25, but for reasons detailed below, its probably something you should automatically buy when purchasing a Synapse 25 and something that is a near automatic purchase for its little brother the Synapse 19. The internal frame is compatible with any Synapse 19 or Synapse 25 that has rails. These rails were intended to be used for the Bihn Cache, an accessory that I have on my Cadet that holds a laptop or tablet, but allows the item to be pulled out for a bag check. Tom Bihn has reverse engineered the rail attachment points to use them as anchors for the internal frame. The result is a wonderfully stable and distinctly different feel to an already great pack.

Here is the business end of the frame:

Twitter Review Summary: If you are buying a Synapse (which you should) or bought one that has rails, this is a no brainer.

One concern I had with an ad hoc internal frame is that it would take up precious cargo room. And while Tom Bihn did not figure out a way to make a Tardis, I am happy to report that the loss of internal storage is minimal. Here is the pack jammed with stuff for a day (a cold day) at the beach.

I was also deeply concerned that the frame would make the back panel stiff or uncomfortable. Again, I am happy to report—while more rigid, the back panel is not painful or crippling. The feeling is something like going from a soft mattress or pillow to a firm mattress or pillow. The back panel now feels a bit more supporting. The "spine" of the panel, a thin bar of aluminum, helps transfer weight from your shoulders to your hips. The frame itself is relatively thin.

Averaged out over different conditions and terrain, the difference is not huge, but it is noticeable. In specific applications, however, it can be a dealmaker. On a day hike during the cold rainy months of March, the weight distribution was not noticeable, perhaps because of my hiking shoes and a couple of extra layers. A May day hike at 90 degrees resulted in just a bit more impact. Instead of chaffing at the shoulders, I had only mild impression marks. The real difference appeared during a long hike on loose beach sand. My hips, ankles, and knees were tired, but my back was not. If you are doing a good deal of vertical hiking or you are walking on unstable ground, the internal frame’s ability to shore things up, keep stuff in place, AND transfer weight to your hips is a big deal and worth the price of admission, even if you are, like me, not a frame pack kind of person.

One thing I wanted to do was to see how heavy I could get the pack naturally (I could have stuck a granite weight I have for my workshop for glue ups in there, but that’s not a realistic carry situation). I jammed in two full sized water bottles. I dropped in a pair of heavy boots. I even loaded up all my heaviest gear (which is noticeably heavier and counterintuitive). Here is the Leatherman Charge TTi with the full bit kit in one of the small item compartments on the Synapse. Even with intentionally overloading the pack, I was still fine, again because a lot of the weight was driven to my hips and not draped over my shoulders. On the beach hike, the difference was quite large.

One of the amazing things about the Synapse design in the centerline water bottle compartment. By placing the compartment where they do Tom Bihn allows you to carry water bottles without feeling like you need a V8. With kids or someone that drinks a lot of water, side water bottle compartments tend to be unbalanced and the result is an unbalanced pack. Here, that never happens, even with an empty and a full water bottle because they are right in the middle of your back.

I was worried that the frame might throw off that wonderful balance, but it didn’t.

In the end, the Bihn Internal Frame is a great accessory. It is, like so many Bihn accessories, something that takes great products and makes them more focused and better a specialization. Personally, right now I don’t hike and carry in a way that can get the most out of the frame. But that’s fine because in a few years when my boys are bigger and our day hikes change into a overnight hikes, I can install the frame and really load up a Bihn pack. For the tiny price of $25, you have the ability to make a pack into something substantially different. If you are thinking of buying a Synapse of either size, there is really no reason not to spend an extra $25 and drop the Internal Frame into your cart at the same time. Note that the same thing can be said for the Cadet and the Cache. I could not be more pleased with my Cadet and adding the Cache to carry my iPad has been one of the best upgrades ever.

Tom Bihn makes some of the best bags out there. They are durable, look nice, are well made, and possess ingenious design touches. But the accessories they are produce are hands down the best available. They make their bags almost infinitely useful. From the Fruedian Slip to the Cache to the amazing high end shoulder strap, Tom Bihn’s accessories make their bags unbeatable. The Internal Frame is yet another accessory that transforms a Bihn bag into something vastly more specialized. They could have made a framed Synapse 25 or 19, but instead, they made it an accessory and priced it at a point that everyone can afford. In doing so you get two bags in one—a frame and unframed version of one of the best bags on the market. Thats not just good design, that is value- and customer-focused good design. And that’s why I really like Tom Bihn’s stuff.