Stitchback Metamorph Pack: Shoulder Straps 

There’s a lot to consider when making your own backpack shoulder straps, and hopefully, this post will demystify the process. For simplicity, I’m going to focus strictly on strap construction for larger, multi-day packs rather than trying to cover the full gamut of bags like daypacks or running vests.

As a quick refresher from my first post, here are our core rules for strap fit:

• DON’T make the strap width too narrow: Narrow straps will dig into your collarbones and shoulders under heavy loads.
• DON’T let the straps sit too close to the neck: Crossing over the thoracic outlet (the space between your collarbone and first rib) can cause nerve and vein compression.
• DO match the natural contour of your body: A proper shape distributes weight evenly, preventing pain and long-term injury.

I’ve broken down strap construction into three critical components: placement on the back, strap shape, and padding. But before we dive into the anatomy, let’s talk about prototyping for this part of the pack.

Prototyping

Testing your fit before cutting into your expensive final materials is vital. Here is the list of prototyping materials I used:

• Cardboard
• Foam (or a foam alternative)
• Stapler
• Quart-size Ziploc bags
• Dry beans (to simulate weight)

When I first did this, I wasn’t creative enough to think of a cheap substitute, so I just used the same 1/4-inch high-density foam intended for my final project. However, testing multiple shapes can quickly eat through your good foam supply. As a reminder, you can find all my materials in my prototyping and materials post.

Budget-Friendly Foam Alternatives

• Heavy Craft Felt: You can hot-glue two layers together to match the thickness and flexibility of real foam.
• Cheap Yoga or Sleeping Mats: Look for budget foam mats at big-box stores or thrift shops.
• Packing Material: Large items are often shipped with high-density foam packing inserts. Check local dumpsters or recycling bins!
• Masking Tape: In a pinch, layers of masking tape stuck to itself can work.

The goal is to replicate the stability and pliability of your final strap. Avoid using thin muslin fabric for your prototype; it is far too flimsy and won’t give you an accurate sense of how the weight will actually ride on your shoulders.

Strap Placement on the Back

OK, now let’s get into the aspects of fit to consider, starting with strap placement on the back of the body. Getting the placement right on the back body is always the very first step, regardless of your final strap shape.

Strap placement is initially determined by the “shoulder strap marking template” provided in your pattern. I cut this template out of cardboard and the prototype straps out of 1/4-inch foam.

To visualize this, imagine a grid laid over the back body. We can adjust the strap placement in three ways:

• Translate along the Y-axis (up and down)
• Translate along the X-axis (medial to lateral or center to outside)
• Rotate (the angle at which the straps pitch outward)

All three of these adjustments work in concert, but let’s break them down individually.

Up-Down Placement

The straps can be positioned higher up toward your head (the cranial or superior direction) or lower down toward your lower back (the caudal or inferior direction).

Regardless of whether you are building a travel pack, school bag, or heavy haul hiking pack, the straps should attach at, or slightly below, the level of your C7 spinous process. The C7 vertebra is the prominent bony bump at the base of your neck when you tilt your head forward. It is the gold-standard landmark used to measure your torso length for commercial packs, and it sits higher up than most people realize.

If the straps attach too low: The pack will pull backward, causing postural changes that strain your spine, put pressure on your thoracic outlet, and drastically increase your risk of injury.

If the straps attach too high: You run into issues with frame size and the pack’s relationship to your hip belt (which we will cover in future posts).

Medial-Lateral Placement

Next, we determine if the straps should sit closer to your spine (medial) or closer to your shoulder joint (lateral). This is a rhetorical question because if you’ve read my previous posts, you know the answer: the straps need to sit laterally, out toward your AC (acromioclavicular) joint.

If the straps attach too close together at the back panel, they will pinch your neck. Because the straps attach so high up on the pack, there simply won’t be enough physical clearance for your neck to fit between them. This causes immediate chafing, rubbing, and painful red marks.

Here’s another example. The rash this hiker is about to produce on the side of her neck is going to be legendary! Let’s hope she also doesn’t pinch a nerve, cause pain to her collarbone, or brusing on her soft neck muscles.

Here’s a screenshot from a recent video from the Backpack Researcher. When straps are properly widened and pushed laterally, they clear the soft tissues of the neck entirely, eliminating the risk of pinched nerves, collarbone bruising, and skin friction.

Rotation

The final element is the angle at which the straps attach. You want them to wrap naturally over the top slope of your shoulders without slipping down.

ℹ️ A quick note on sternum straps: a sternum strap should never be used as a crutch to force improperly angled shoulder straps to stay on your body. You should be able to wear your pack comfortably without one.

Take the time during prototyping to play with angling the attachment points. Matching the exact slope of your own shoulders generally yields the best results.

Putting it all together

Every body shape is unique. Whether you have narrow, flat shoulders (left) or a wider frame with sloping shoulders (right), Make Your Own Gear (MYOG) patterns allow you to customize the pack to fit you.

For this specific pattern, ensure the top attachment point aligns with your C7 vertebra, then widen or narrow the back panel attachment points until the straps naturally rest securely on your unique shoulder frame. Don’t forget to adjust the angle of attachment to match the angle of your shoulder slope.

Shape

When it comes to strap geometry, there are three primary options:

• J-Shape: A classic, traditional straight-down strap that curves out slightly at the bottom.
• S-Shape: A wavy design traditionally meant to curve inward around the neck, over the collarbone, and then flare outward to accommodate a bust or large chest.
• Hybrid/Natural Shape: A modern design that combines elements of both.

Personally, I don’t love the traditional S-shape. It often assumes the straps sit close to your neck, which can crush your collarbone as it comes over the shoulder. If you correctly move the strap attachment points away from the neck laterally, the S-shape often becomes unnecessary. That said, I haven’t studied thousands of body types, so I won’t say S-straps are never needed. I just haven’t seen a convincing argument for them on my own builds.

The most critical factor in strap shape is torsion. When weight is loaded into the pack, gravity pulls straight down. You want that downward force distributed evenly across the entire width of the strap. If your strap shape is wrong, the inner or outer edge will lift, flip away from the body, or twist, causing severe pressure points. Always test your prototype strap shape with real weight in the pack to ensure it sits completely flat against your chest.

ℹ️ Pro-Tip: The padded portion of your strap should be long enough that the adjusting buckle sits well below your armpit.

Don’t be like this person. The buckle right at your armpit? Chafing is definitely going to happen. Deuter packs actually provides a good explination of how not to fit your straps!

Padding

Now to the last feature that can impact comfort. Padding thickness comes down to personal preference and your intended pack weight. The heavier the load, the denser and more supportive your padding needs to be.

The pattern recommends 1/4-inch high-density EVA foam. If you want a plushier feel, you can certainly go thicker, but never use cheap, flimsy open-cell foam from a standard craft store. Open-cell foam (like mattress topper or cushion foam) will instantly crush flat under a heavy load, leaving you with the comfort equivalent of raw webbing. You need a closed-cell foam that actively resists compression to distribute weight.

If you want to create something plusher, you can layer different foam densities together:

• The Body Side: Use a softer foam (like a 2 lb. density cross-linked polyethylene) against your chest for comfort (here and here).
• The Outer Side: Laminate it to a firmer, high-density foam (like a 4 to 6 lb. EVA foam) to provide structural rigidity and distribute the load. The foam I used from the Foamary would work here.

Extras

Load Lifters

I genuinely dislike the name “load lifters” because it misleads beginners into thinking these straps mechanically lift the weight off their back. They don’t. The true purpose of a load lifter is to pull the top of the pack closer to your torso, preventing it from leaning away from you. We really should rename them “body huggers” or the “make-your-pack-fit-right-o-rater.”

In the time it took me to write this post, of course, the Backpack Researcher came out with a video about Load Lifters! I did admit though at the beginning that all my research basically came from this individual.

Sternum Straps

As mentioned before, a sternum strap should not be acting as a structural ratchet to keep your shoulder straps from falling off your arms.

However, if you do include sterum straps, the sternum strap should sit approximately 1 to 2 inches below your collarbone, directly inline with the muscular front of your shoulders rather than down by your armpits. It should stabilize the load without choking you or digging into sensitive breast tissue.

Pattern

To give you a real-world example of how these principles work, let’s look at how the original pattern fit out-of-the-box, and the exact modifications I made for myself and my partner, Ryan.

Original Fit

Using the provided strap placement guide and the longer of the two patterns, we hit two major fit issues right away:

You’ll notice that the straps are pushing into our necks (circled in white) and pressing heavily into the soft tissue of our shoulders and going over the thoracic outlet.

Instead of contouring over the shoulder smoothly, the straps buckled, creating an awful-looking gap or “bump” behind the shoulder rather than sitting flush.

Adjusting the Strap Shape

To fix this without overcomplicating things, I converted the S-shape into a more natural, hybrid shape. I literally sliced across the top portion of the pattern piece, flipped it, and redrew the lines. I kept the lower half of the strap identical to the pattern but altered the upper half so that the angle between the upper and lower sections was between 155° to 160°.

Strap Placement Adjustment for Me

I had to shift my straps outward (laterally) by 1-1/2 inches. In order to have enough room for sewing on the straps later, I made sure I had at least 5/8 inches along the side. I needed to widen my strap placement guide by 1/4 inch. I kept the angle for the strap placements the same. Finally, I shortened the overall strap length by 2 inches.

The strap completely clears my neck and thoracic outlet, eliminating that annoying friction and pressure, and the hideous gap behind my shoulder is gone.

The new straps contour smoothly from the back panel, across my shoulders, and neatly around my arms.

Strap Placement Adjustment for Ryan

Ryan required even more dramatic adjustments to fit his frame. First, I needed to shift his straps outward 2-3/8 inches. This meant I needed to widen his strap placement guide by 1-1/8. This time, I made sure the side of the strap placement guide was the same as the original, since the change was so dramatic. Finally, I adjusted the angle of the strap placement a little bit. I moved the center point up 1/16 inch to make the angle slightly steeper.

A night-and-day difference in comfort. No more neck-digging, the wrinkles are gone, and the straps sit completely flush against his torso.

Ryan’s never had a pack fit so nicely.

Putting it all Together

The podcast is a great summary / review of everything I’ve talked about so far in this post. And hopefully now that you have a bit more knowledge, the podcast will make sense. They just go off about foam and thickness and sewing and don’t always describe things in ways a beginner would understand.

Personal Aside

First, I think I did too good of a job on picking out his fabric from Spoonflower, because Ryan ended up on the menu for a very cute broadtail hummingbird.

Second, my jaw dropped when I watched this video. This is crazy groundbreaking for the industry and what an incredible resource for people who want to create luxury clothing. I think seeing high-end fashion like this puts my skills and efforts into perspective. I have so much respect for all the talented people that can do such amazing stuff with clothing.