Osprey Seral 4L Bike Hydration Lumbar Pack
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Osprey Size Chart
How to measure: Find your iliac crest (top of hip bone). On the back of your neck, find the C7 vertebra (touch your chin to your chest — the large protruding bone at the base of your neck). Measure from C7 to the iliac crest to determine your torso length.
Men's Sizing
| Torso | 14" 35.5cm |
15" 38cm |
16" 40.5cm |
17" 43cm |
18" 46cm |
19" 48cm |
20" 51cm |
21" 53cm |
22" 56cm |
23" 58.5cm |
24" 61cm |
25" 63.5cm |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| M Outdoor | ||||||||||||
| Aether Plus / Aether | — | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | S/M or L/XL | L/XL | L/XL | — | — |
| Aether Pro | — | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | L/XL | L/XL | L/XL | — | — |
| Atmos AG | — | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | S/M or L/XL | L/XL | L/XL | — | — |
| Atmos AG LT | — | — | — | S/M | S/M | S/M | S/M | L/XL | L/XL | L/XL | — | — |
| Talon 11, 22, 26, 33 (2025) | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Talon 44 (2025) | — | — | S/M | S/M | S/M | S/M or L/XL | L/XL | L/XL | L/XL | L/XL | — | |
| Talon / Talon Pro / Talon Velocity | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | L/XL | L/XL | — | — | ||
| Talon 6 | O/S — Hipbelt Fit Range: 25–50" (64–127 cm) | — | — | |||||||||
| Rook | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Volt | — | — | — | O/S | O/S | O/S | O/S | OS | — | — | ||
| Exos / Exos Extended Fit | — | — | — | S/M | S/M | S/M or L/X | S/M or L/XL | L/XL | L/XL | L/XL | — | |
| Exos Pro | — | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | L/XL | L/XL | L/XL | — | |
| Kestrel | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | S/M or L/XL | L/XL | L/XL | — | ||
| Osprey UNLTD AG 32 | — | — | — | S/M | S/M | S/M or L/XL | S/M or L/XL | L/XL | L/XL | L/XL | — | |
| Stratos | — | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | |
| Soelden Pro / Soelden | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Kamber 20, 30 | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| M Hydration | ||||||||||||
| Manta / Skarab | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Duro LT, 6, 1.5 | Sm (30–35" / 75–90 cm) · Med (35–41" / 90–105 cm) · Lg (41–47" / 105–120 cm) — Chest | — | — | — | — | — | ||||||
| Duro 15 | S/M (30–41" / 76–104 cm) · M/L (41–47" / 104–119 cm) — Chest | — | — | — | — | — | ||||||
| Raptor / Raptor Extended Fit / Syncro / Siskin / Katari | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | |
| M Travel | ||||||||||||
| Farpoint Travel Pack | — | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | |
| Farpoint Trek | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Ozone Duplex (M) | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
Unisex Sizing
| Torso | 14" 35.5cm |
15" 38cm |
16" 40.5cm |
17" 43cm |
18" 46cm |
19" 48cm |
20" 51cm |
21" 53cm |
22" 56cm |
23" 58.5cm |
24" 61cm |
25" 63.5cm |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Outdoor | ||||||||||||
| Hikelite 18, 26 | O/S | O/S | O/S | O/S | O/S | O/S | O/S | O/S | — | — | — | |
| Hikelite 28, 32 | — | S/M | S/M | S/M | S/M or M/L | S/M or M/L | M/L | M/L | M/L | — | — | |
| Glade 5, 12 | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Firn 18, 28 | — | S/M | S/M | S/M | S/M or M/L | S/M or M/L | M/L | M/L | M/L | — | — | |
| Osprey Sportlite 15, 20 | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | — | — | |
| Osprey Sportlite 25, 30 | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | — | |
| Mutant 22 | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — | |
| Mutant 52, 38 | S/M | S/M | S/M | S/M | S/M or M/L | M/L | M/L | M/L | M/L | — | — | |
| Zealot 30 | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — | |
| Zealot 45 | S/M | S/M | S/M | S/M or M/L | M/L | M/L | M/L | M/L | M/L | — | — | |
| Hydration | ||||||||||||
| Duro Dyna Belt | O/S — Hipbelt Fit Range: 24–45" (60–115 cm) | |||||||||||
| Raptor Pro | — | — | — | O/S | O/S | O/S | — | — | — | — | — | |
| Savu | O/S — Hipbelt Fit Range: 26–50" (66–127 cm) | |||||||||||
| Seral | O/S — Hipbelt Fit Range: 26–50" (66–127 cm) | |||||||||||
| Bike Commute | ||||||||||||
| Radial | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Metron 26, 24 | — | O/S | O/S | O/S | O/S | O/S | O/S | O/S | — | — | — | |
| Child Carrier | ||||||||||||
| Poco SLT / Poco LT / Poco / Poco Plus / Poco Premium | — | O/S | O/S | O/S | O/S | O/S | O/S | O/S | — | — | — | |
Kid's Sizing
| Torso | 11" 28cm |
12" 30.5cm |
13" 33cm |
14" 35.5cm |
15" 38cm |
16" 40.5cm |
17" 43cm |
18" 46cm |
19" 48cm |
20" 51cm |
21" 53cm |
22" 56cm |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ace 75 (age 12–17) | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — |
| Ace 50 (age 8–14) / Ace 65 (age 10–17) | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — |
| Ace 38 (age 5–11) | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — | — | |
| Jet 18 (age 8–14) | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — | |
| Hydrajet (age 4–12) | O/S | O/S | O/S | O/S | O/S | — | — | — | — | — | — | |
| Daylite JR (age 4–12) | O/S | O/S | O/S | O/S | O/S | — | — | — | — | — | — | |
| Moki (age 4–12) | O/S | O/S | O/S | O/S | O/S | O/S | — | — | — | — | — | |
| Talon / Tempest JR (age 8–14) | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | — | |
| Raptor Jr / Raven Jr (age 6–14) | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — |
Women's Sizing
| Torso | 11" 28cm |
12" 30.5cm |
13" 33cm |
14" 35.5cm |
15" 38cm |
16" 40.5cm |
17" 43cm |
18" 46cm |
19" 48cm |
20" 51cm |
21" 53cm |
22" 56cm |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| W Outdoor | ||||||||||||
| Ariel Plus / Ariel | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Ariel Pro | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Aura AG | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Aura AG LT | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Tempest 11, 22, 26, 33 (2025) | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Tempest 44 (2025) | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | — | — | |
| Tempest / Tempest Pro / Tempest Velocity | — | — | — | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | — | — | |
| Tempest 6 | O/S — Hipbelt Fit Range: 24–44" (61–112 cm) | — | — | |||||||||
| Renn | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Viva | — | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | |
| Eja / Eja Extended Fit | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Eja Pro | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Kyte | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Osprey UNLTD AG 32 | — | — | XS/S | XS/S | XS/S | XS/S or M/L | XS/S or M/L | M/L | M/L | M/L | — | — |
| Sirrus | — | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | |
| Sopris Pro / Sopris | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Kresta 20, 30 | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| W Hydration | ||||||||||||
| Mira | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | |
| Skimmer | — | — | — | — | O/S | O/S | O/S | O/S | — | — | — | |
| Dyna LT, 6, 1.5 | Sm (26–30" / 65–75 cm) · Med (30–35" / 75–90 cm) · Lg (35–41" / 90–105 cm) — Chest | |||||||||||
| Dyna 15 | S/M (26–35" / 66–90 cm) · M/L (35–41" / 90–104 cm) — Chest | |||||||||||
| Raven / Raven Extended Fit / Sylva / Salida / Kitsuma | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | — | |
| W Travel | ||||||||||||
| Fairview Travel Pack | — | — | — | — | O/S | O/S | O/S | O/S | O/S | — | — | |
| Fairview Trek | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
| Ozone Duplex (W) | — | — | — | O/S | O/S | O/S | O/S | O/S | O/S | — | — | |
How to measure: Measure around the hips at the iliac crest, not the waist. The padded portion should wrap well around the hips, leaving a gap of 3" to 6" between the tips of both hip pads when securely tightened.
Fixed Hipbelt Sizing
XS24–25" / 60–114 cm
S24–25" / 60–114 cm
S/M26–45" / 65–114 cm
M27–48" / 69–121 cm
M/L28–50" / 70–127 cm
L29–55" / 72–140 cm
O/S25–50" / 64–127 cm
S/M EF17–20.5" / 43–52 cm
L/XL EF19.5–23" / 49–58 cm
O/S EF40–70" / 101–177 cm
WXS/S EF13.5–17" / 34–43 cm
WM/L EF16–19.5" / 40–49 cm
EF = Extended Fit
Adjustable Hipbelt Options
Packs with Fit-on-the-fly™ adjustable hipbelt allow you to fine-tune sizing for optimal carry performance:
- Atmos AG / Aura AG
- Volt / Viva
- Ace (Kids)
- Poco Child Carrier
Extended Fit (EF) Overview
Extended Fit packs add new sizing to provide people in larger bodies the same uncompromised performance. EF hipbelts fit up to 70" hips.
Longer Hipbelt Padding
Substantially longer padding provides comfort, support and stability for larger body shapes.
Repositioned Hipbelt Pockets
Hipbelt pockets shifted forward for practical, easy-to-reach access.
Extended Shoulder Straps
Longer shoulder straps distribute the load evenly and comfortably.
Longer Sternum Strap
Enhances stability without being restrictive.
How to measure: Measure the circumference of your chest at its widest part — across your chest/bust, just below the armpits and around your back. Then locate your vestpack and use your chest measurement to choose the best size.
Vestpack Sizing — Running
| Vestpack | Sizes Offered | Chest Circumference |
|---|---|---|
| Duro 6 / Duro 1.5 / Duro LT | Men's Small · Men's Medium · Men's Large | 34.5–37 in / 88–94 cm · 37–42.5 in / 94–108 cm · 42.5–46.5 in / 108–118 cm |
| Duro Pro 7 / Duro Pro 10 | Men's Small · Men's Medium · Men's Large | 34.5–37 in / 88–94 cm · 37–42.5 in / 94–108 cm · 42.5–46.5 in / 108–118 cm |
| Dyna 6 / Dyna 1.5 / Dyna LT | Women's Small · Women's Medium · Women's Large | 31.5–35 in / 80–89 cm · 35–38.8 in / 89–98 cm · 38.5–42.5 in / 98–108 cm |
| Dyna Pro 7 / Dyna Pro 10 | Women's Small · Women's Medium · Women's Large | 31.5–35 in / 80–89 cm · 35–38.8 in / 89–98 cm · 38.5–42.5 in / 98–108 cm |
| Past-Season Sizing | ||
| Duro 6 / Duro 1.5 / Duro LT (Past-Season) | Men's Small · Men's Medium · Men's Large | 29.5–35 in / 75–90 cm · 35–41 in / 90–105 cm · 41–47 in / 105–120 cm |
| Duro 15 (Past-Season) | Men's S/M · Men's M/L | 29.5–41 in / 75–105 cm · 41–47 in / 105–120 cm |
| Dyna 6 / Dyna 1.5 / Dyna LT (Past-Season) | Women's Small · Women's Medium · Women's Large | 26–29.5 in / 65–75 cm · 29.5–35 in / 75–90 cm · 35–41 in / 90–105 cm |
| Dyna 15 (Past-Season) | Women's S/M · Women's M/L | 26–35 in / 65–90 cm · 35–41 in / 90–105 cm |
Vestpack Sizing — Biking
| Vestpack | Sizes Offered | Chest Circumference |
|---|---|---|
| Escapist Velocity 3 | Unisex S/M · Unisex L/XL | 26.5–36 in / 67–92 cm · 35–47 in / 89–119 cm |
| Escapist Velocity 6 | Unisex S/M · Unisex L/XL | 26.5–36 in / 67–92 cm · 35–47 in / 89–119 cm |
How to Fit Your Pack
1. Position the Pack
Completely loosen the hipbelt, harness and load-lifter straps. Load the pack with 10–20 lbs / 4–5 kg of gear. Put the pack on and make sure the hipbelt is centered and rests over the hipbone. The hipbelt padding should sit halfway above/below the hipbone.
2. Buckle the Hipbelt
Buckle and tighten evenly using the cross-body Ergo-Pull. The padding should wrap around the hips with approximately 1–3 in / 2.5–6 cm of webbing between the buckle and hipbelt when tightened.
3. Tighten Shoulder Straps
Tighten by pulling the shoulder harness straps down and back. The harness straps should wrap fully around the shoulders with no gaps between the pack and your back.
4. Tighten Load Lifters
This pulls the pack close to the body and helps stabilize the load. If the torso length is adjusted correctly, load lifters will sit between a 30° to 60° angle and align naturally with the shoulder straps.
5. Check Torso Length
Locate the harness yoke (where harness straps come together near the base of the neck) and the C7 vertebra. The yoke should be 1–2 in / 2.5–5 cm below the C7 vertebra.
6. Buckle the Sternum Strap
Adjust to approximately 2 in / 5 cm below the collarbone. This helps stabilize the pack without restricting breathing.
Signs You Need a Different Size
- Load lifters angled below/above 30–60 degrees
- Yoke to C7 vertebra distance is more than 2 in / 5 cm or less than 1 in / 2.5 cm
- There is a gap between the harness and back of the shoulder
- The hipbelt "tops out" or doesn't provide enough coverage
- Padded part of shoulder straps tops out below the armpits
Women's-Specific Fit
Osprey has been designing packs for women for over 25 years. Women's-specific features include:
- Shorter torso length — tailored to fit female body proportions
- Narrower, shorter harness — curves designed to accommodate most women's necks, shoulders and chests
- Curved hipbelt — wraps naturally around women's hips for better load stabilization and support
- Add To Cart For Final Price
Seral 4L Bike Hydration Lumbar Pack
Hydrate fast and ride light with this compact, stable lumbar-style bike pack featuring an integrated low-profile Hydraulics™ 1.5L LS Reservoir. A magnetic attachment secures the bite valve to the hipbelt, while a bike-specific airmesh wrap hipbelt and close-to-body AirScape™ backpanel deliver breathable, bounce-free comfort. Vertical straps hold a chin guard or extra layer for added versatility.
Reservoir Included
Drinking while riding has never been easier with the included Hydraulics™ LS Lumbar 1.5 Reservoir, smart hose routing and a magnetic bite valve attachment.
Rider-Focused Features
Enhance every ride with stabilizing side compression, dual tuckaway front accessory straps designed to secure a chin guard or extra layer, and more.
AirScape™ Backpanel
Pedal with the comfort and stability of a mesh-covered, extra-thick ridged foam backpanel featuring a center airflow channel.
bluesign® PRODUCT
This product meets bluesign® PRODUCT requirements, which means materials and components have been selected that adhere to rigorous third-party environmental and social criteria during production.
AirScape™ Backpanel
Mesh-covered, extra-thick ridged foam with center airflow channel provides comfortable, stable, close-to-body carry Made with 50% recycled EVA foam
Hipbelt
Breathable airmesh wrap hipbelt provides stability on rough terrain Crossbody ErgoPull hipbelt system ensures snug fit for optimal load support
MAIN
bluesign® APPROVED, 100% recycled 300D polyester, DWR treatment made without PFAS
LINING
bluesign® APPROVED, 100% recycled 210D nylon, DWR treatment made without PFAS
MESH
Backpanel & Hipbelt Mesh: bluesign® APPROVED, 100% recycled polyester WARNING: This product can expose you to chemicals including dimethylformamide, which is known to the State of California to cause cancer. For more information, go to oehha.ca.gov/proposition-65/about-proposition-65
Shipping Policy
Components:
All component items (wheels, drivetrains, suspension, brakes, etc.) ship within 1–4 business days of purchase.
Bicycles:
Complete bikes typically ship within 2–3 weeks due to build, tuning, and inspection times. You will receive tracking information as soon as your order is ready to ship.
Riding Gear & Apparel:
Riding gear and apparel orders (helmets, jerseys, gloves, etc.) ship within 1–3 business days.
Returns & Exchanges:
If you received the wrong size or wish to exchange an item, it must be returned in original condition—unused, uninstalled, and with all packaging intact.
For full details, please see our Refund Policy before initiating a return.
