Michael Turner
If you plan to carry more than 15 kg for multi-day hikes, choose an internal-frame pack with aluminum or carbon stays and a properly sized hip belt to transfer roughly 60–80% of the load to the pelvis.
Construction notes: internal stays sit between the backpanel and main compartment, providing vertical stiffness and improved load transfer. Typical stay materials: aluminum stays ~150–300 g (durable, easy to repair), carbon/composite ~80–180 g (lighter, higher cost), molded polymer frames ~200–400 g (flexible, budget-friendly). Structural components add approximately 400–1,000 g versus frameless designs; expect trade-offs between weight and stability.
Fit and adjustment: measure torso length from C7 vertebra to the iliac crest and choose S (38–43 cm), M (43–48 cm), or L (48–53 cm) accordingly. Position the hip belt on the iliac crest so the belt bears the majority of weight; aim for a 10–12 cm contact width on the hips. Set load-lifter straps to about 30°–45° so the top of the load sits 2–5 cm behind the shoulders; shoulder straps should carry no more than 10–20% of total mass when fitted correctly.
Capacity and packing strategy: typical volumes – 20–35 L for day use, 35–50 L for overnight, 50–70 L for 2–4 day trips, 70+ L for extended expeditions. Pack heaviest items centered and close to the spine, medium-weight items around them, and bulky/less dense gear low or in external compartments. Use compression straps to minimize sway; keep carried mass under ~25–30% of body weight for prolonged travel to preserve stamina and reduce injury risk.
Practical care and checks: inspect frame rivets, hip-belt stitching and webbing regularly, and test zippers and buckles before outings. Clean fabric per manufacturer guidelines (gentle detergent or hand wash), air dry away from direct heat. If frame deformation, cracked stays or seam failure is detected, retire the pack from load-bearing use until repaired or replaced.
Internal vs external frames: choosing the right frame for multi-day hiking
If you expect to carry 25–35 kg or frequent bulky/irregular cargo (game, fuel cans, camera rigs), opt for an external-frame pack; if your typical load is 6–20 kg on maintained trails or mixed scrambling, pick an internal-frame design.
Load and terrain thresholds
Numbers to use when deciding: day-to-day loads under 12 kg = internal frame recommended; 12–25 kg = either, based on comfort and torso fit; consistently above 25 kg = external frame preferred. Capacity guidance: 40–65 L suits internal-frame long trips; 65–90+ L suits external-frame hauls. External-frame systems perform better on straight, long approaches and when carrying uneven or heavy gear. Internal-frame configurations keep mass closer to the torso, improving balance on narrow ridgelines, steep scrambles and technical trail sections.
Fit, carry and field practicality
Target hipbelt load transfer of 60–80% so hips bear most of the mass; test any loaded pack for 10–15 minutes on a slope to confirm that transfer. Typical frame mass ranges: internal stay assemblies ~200–600 g; external frame assemblies ~600–1,200 g (varies by material). Choose an internal-frame model if you need low center of gravity and quick maneuvering; choose an external-frame model if you need maximum ventilation behind the torso, easy attachment points for odd-shaped loads, and simpler field repairs. Carrying tips: use load lifters and sternum strap to fine-tune balance with internal stays; with external frames arrange a stable load shelf and strap heavier items low and centered.
Choose shape and material to match load: rigid vertical stays for heavy loads, polymer sheets for light loads
For sustained loads above ~18 kg use a rigid vertical-stay support (dual or continuous stays) plus a stiff hip-transfer plate; for loads under ~12 kg a molded polymer sheet or thin composite offers acceptable stability at lower mass.
Shape: how geometry controls load capacity and dynamic stability
Vertical stays (two parallel rods or bars) concentrate bending stiffness along the torso axis, allowing 60–80% of carried mass to be routed to the hip belt when the lumbar plate and hip belt are matched to torso length; this maximizes load capacity and minimizes upper-body sway. Continuous-sheet frames distribute load across a broad lumbar surface, reducing local pressure and improving comfort for mid/heavy loads but require greater material thickness to reach the same torsional stiffness as discrete stays. Narrow-profile frames (20–25 cm chest width) lower wind torque and keep the center of mass closer to the spine, improving single-track stability; wider platforms (25–35 cm) increase lateral support and are better for bulky, high-center loads. Recommended torso-fit tolerance: frame height within ±2 cm of measured torso length to preserve intended load transfer and prevent shoulder levelling or pelvic tipping.
Materials: stiffness, weight, fatigue and practical thresholds
Aluminum alloys (e.g., 6061) offer modulus ~69 GPa and high yield strength for minimal added weight; typical aluminum stays add ~150–350 g and maintain stiffness under repeated flexing–choose aluminum for repeated heavy loads (≥18 kg). Spring steel delivers highest fatigue life and torsional stiffness (modulus ~200 GPa) but at a weight penalty (~350–600 g); use steel only if cost and weight are acceptable. Carbon-fiber composites provide the best stiffness-to-weight; composite stays or bowed frames often weigh 80–200 g while matching aluminum stiffness, but inspect joints for delamination and avoid concentrated bending at bonded terminations; suitable for high-performance lightweight loads (8 mm is needed to approach metal-stay stiffness. Expect polymer sheets to lose stiffness in heat and to creep under constant high load; avoid long-term loads near their yield stress.
Practical selection summary: choose metal or carbon vertical stays + rigid lumbar transfer for multi-day loads above 15–18 kg; choose composite or polymer-sheet supports for base weights under ~12–15 kg. Match hip-belt width and pad stiffness to the frame’s transfer characteristics and verify torso fit ±2 cm. For a care package or celebratory resupply, consider including a nice red wine for a gift.
Step-by-step fitting: adjust torso length, hipbelt and load lifters for comfort
Set torso length so the shoulder straps sit 2–3 cm below the C7 vertebra and the lumbar pad contacts the top of the pelvis; aim for shoulder harness contact at the upper trapezius without pinching.
Measure torso length
- Stand upright. Locate C7 (most prominent neck vertebra) and the top of the iliac crest (pelvic ridge).
- Measure along the spine from C7 to the iliac crest; record in cm. Typical sizing bands: Small 38–43 cm, Medium 43–48 cm, Large 48–53 cm.
- If the carry system is adjustable, set the harness slider to the measured value ±1 cm. If non-adjustable, choose the next size up rather than down.
Fit hipbelt and load lifters – sequence and target numbers
- Load the pack with the weight you intend to carry while walking (use ~75% of planned max for multi-day loads).
- Put the carrier on. Position the hipbelt so the foam cups sit directly over the iliac crest; the top edge of the belt should be approximately 0–2 cm above the crest.
- Tighten the hipbelt by pulling the webbing forward until the belt transfers 60–80% of the total weight to the hips (for heavy loads >15 kg aim closer to 70–80%).
- Fasten the shoulder straps and pull them snug so they remove the slack but do not lift the hipbelt off the pelvis. You should be able to slide one finger under each shoulder strap.
- Set load lifters so the strap angle is about 10–20° above horizontal (visually a 30–45° angle from the pack to the shoulder). Tighten until the top of the load tilts toward the back of the neck by ~1–2 cm–this keeps mass close to the spine while preventing shoulder pressure.
- Adjust the sternum strap 4–6 cm below the collarbone; tighten only enough to stabilize the shoulder straps, not to compress the chest (breath must be unrestricted).
- Dynamic test: walk briskly for 50–100 m, climb several steps and simulate lifting a foot over obstacles. If hips feel unloaded, increase hipbelt tension in 1–2 cm increments. If shoulders hurt, increase hipbelt carry percentage or loosen load lifters slightly.
- For loads under 10 kg aim for hips to carry ~60–70%; for 10–20 kg aim ~65–75%; for >20 kg increase to ~75–80% and re-check spine alignment and padding pressure points.
- If pressure points appear on the iliac crest, shift hipbelt up to sit on fleshier part of pelvis, or add a thin foam spacer between pad and hipbone to spread load.
When final adjustments are made, mark the harness slider position with a tiny piece of tape for repeatable setup; if comparing carry systems or sizing methods, also review unrelated gear compatibility such as best umbrella stroller fpr big baby.
Field repairs and maintenance for aluminum, carbon and plastic frames on packs
Carry a compact repair kit: hex keys (3, 4, 5 mm), 8 mm and 10 mm open wrenches, small adjustable wrench, pliers, multi-bit screwdriver, spare M4 and M5 bolts, 3–4 mm pop rivets (10 pcs), 3–5 m paracord, 10–15 heavy-duty zip ties, 2-part epoxy (30–60 min cure), cyanoacrylate with accelerator, epoxy putty, small file, 80/120/220 grit sandpaper, duct tape, cloth tape, and a tube of silicone zipper lubricant. Add a short tent-pole section or a rigid carbon/aluminum splint as an emergency strut.
Aluminum frame repairs – detection and fixes: inspect bends, cracks and weld areas after any heavy impact. Hairline cracks show as whitish oxidised lines; tap-test will sound dull over a crack. For a temporary fix, straighten minor bends using a wooden block and rubber mallet, support the opposite side with the splint and secure with hose clamp and tape. For permanent field repair when welding is impossible, clean paint and corrosion back to bare metal with 120 grit, rivet a 1.5–2.0 mm aluminium patch plate using 3–4 mm pop rivets placed 20–30 mm apart, then seal edges with epoxy or marine sealant. Apply a thin coat of corrosion inhibitor (Boeshield T-9 or light oil) to exposed aluminium after repair.
Carbon stays – emergency containment and structural repair: do not repeatedly bend carbon elements. If a stay shows a dull tap or visible delamination, splint immediately: align the section, wrap tightly with a rigid tent-pole segment or a short length of thin wall aluminium tubing, then tape and tape-over with epoxy-impregnated cloth if available. For a durable workshop repair, sand 80–120 grit to remove resin gloss, clean with isopropyl, lay two to three layers of carbon cloth with a compatible two-part epoxy (30–60 min work time), cure 24+ hours at ambient temperature; use microballoon-filled epoxy to fair gaps. Avoid drilling through delaminated sections; if attachment point fails, replace with a new stay.
Polymer/plastic frame inserts – diagnostics and repair methods: identify material (HDPE, nylon, polypropylene) by flexibility and melting behaviour; stress-cracks usually appear near bends and attachment tabs. For hairline splits, use cyanoacrylate with accelerator for a fast bond; for load-bearing breaks, use plastic welding with rod matching the substrate (polypropylene rod for PP, nylon rod for nylon) or apply a two-part structural epoxy with a backer plate riveted across the break. When welding tools aren’t available, fabricate a through-bolt splice using a metal flat plate on both sides, secure with M5 bolts and lock-nuts; pad plates with thin rubber to avoid stress concentrations.
Hardware, straps and attachment points: bring spare buckles equal to strap widths (20–40 mm), replacement webbing loops, and a few stainless steel washers and lock-nuts. Replace stripped bolts with slightly longer M4/M5 bolts and matching lock washers. Use medium-strength removable threadlocker on steel bolts in workshop repairs; avoid threadlocker on stainless or polymer fasteners unless specified by manufacturer. For torn load straps, use a short length of tubular webbing stitched or lashed around the frame with paracord as a temporary sling.
Preventive maintenance schedule and cleaning: after salty or muddy exposure rinse with fresh water, wipe down with mild soap, fully dry before stowing. Every 6–12 months inspect attachment rivets, welds, and stays; sand any surface corrosion on aluminium and touch up with rust-inhibiting paint or thin lacquer. For carbon, scan for soft spots or delamination; flex test suspect areas gently. Re-lube zippers with silicone, and replace worn foam or hipbelt padding seams with outdoor-grade thread and backstitch repair or use seam-grip-type adhesive for joint patches.
Field improvisation techniques: use fishing line and a curved safety needle to stitch through torn fabric around frame channels; use duct tape wrapped in several layers as a temporary load-bearing pad; secure a broken stay with a tent-pole section lashed with paracord and protected by heat-shrink tubing. For frame-to-bag separation, stitch or rivet a replacement webbing tab; a 20–30 mm wide webbing loop plus two M5 bolts through a patch plate will restore main attachment quickly.
For selection tips on models that accommodate umbrella carry and accessory repairs, see best backpack to carry umbrella.
