How to Wash a Backpack
The spin cycle deforms polyethylene frame sheets. Open-cell foam padding takes days to dry and grows mould inside. Detergent residue destroys DWR coating. Remove the frame, hand wash cool, dry completely upside down.
The Chemistry
Backpacks are composite products — the shell fabric, the structural frame, the foam padding, the zippers, and the internal coatings all have different material properties and react differently to water and agitation. The shell fabric is usually nylon (Nylon 6 or Nylon 6,6 — polyamide polymers with slightly different crystal structures) or polyester. Cordura fabric, used in premium packs, is a high-tenacity nylon with a more compact molecular structure giving higher abrasion resistance. Both nylon and polyester are naturally hydrophobic and carry a DWR (durable water repellent) coating — a fluoropolymer applied to the outer face of the fabric. Regular detergent leaves surfactant residue on the fabric after rinsing, and this residue suppresses the hydrophobic effect of DWR, causing the bag to absorb water instead of repelling it. Internal coatings are a critical vulnerability. Laptop sleeves, hydration reservoir compartments, and the base of many packs use a polyurethane (PU) film coating. This coating follows the same hydrolysis pathway as tent coatings — water attacks the urethane-ester bonds over time. Machine washing dramatically accelerates this, especially with any detergent that changes the pH of the wash water away from neutral. The structural frame — on any pack with a frame sheet — is almost always high-density polyethylene (HDPE) or low-density polyethylene (LDPE), typically around 1–2mm thick. Polyethylene has no formal glass transition temperature in the conventional sense (it is semi-crystalline), but it softens meaningfully from around 60°C and can take on permanent set deformation at lower temperatures under sustained load. A machine wash cycle — even cold — combined with the centrifugal force of the spin cycle can deform the frame sheet if the bag folds onto itself. External frame packs with aluminium stays present a different problem: water trapped between the stay and the fabric sleeve encourages galvanic corrosion if the sleeve is nylon and there are any metal rivets present. Foam padding in shoulder straps and back panels is usually open-cell polyurethane foam. Open-cell foam absorbs water like a sponge and compresses significantly in a spin cycle. After machine washing, the foam may not fully dry for 24–48 hours inside the fabric sleeve — creating ideal conditions for mould growth inside the padding that is invisible from the outside. Zippers with metal teeth (common on premium zipper pulls) can have teeth bent slightly out of alignment by machine agitation, causing binding. YKK and similar coil zippers are made from nylon monofilament — these are more tolerant of machine washing but the nylon monofilament can stiffen if wax lubricant is washed out.
Step-by-step
- 1
Empty all pockets and remove the frame sheet and stays
Empty every compartment — check all pockets including the hidden ones on shoulder straps. Remove any PE or HDPE frame sheet, aluminium stays, or carbon-fibre stiffeners. Washing with the frame in place risks permanent deformation from the spin cycle.
- 2
Shake out loose dirt and brush off dried mud
Dry mud brushes off cleanly — wet mud smears into the fabric weave and is harder to remove. Use a stiff brush on the shell and base. Turn the bag upside down over a bin to remove debris from the main compartment. This step reduces the amount of dirt the water has to deal with.
- 3
Spot clean with a soft brush and diluted mild detergent
For most cleaning needs, a soft brush with cool water and a small amount of diluted mild detergent is all that's needed. Work on the dirty areas (base, shoulder strap surfaces, back panel). A 5:1 ratio of water to dish soap is sufficient. Avoid concentrating detergent on DWR-treated areas of the shell.
- 4
Hand wash in cool water for heavy soiling
For very dirty packs, partially fill a bathtub with cool water and a small amount of technical wash (Nikwax Tech Wash or similar non-residue cleaner). Submerge the pack and agitate gently by hand for 10–15 minutes. Focus on the base, back panel, and shoulder straps. Avoid vigorous scrubbing of coated or laminated surfaces.
- 5
Rinse thoroughly — all detergent must be removed
Rinse with clean cool water until no soap foam is visible. Detergent residue on the shell fabric suppresses DWR water repellency. For the interior, rinse carefully and drain fully — tilt the bag in every direction to ensure water drains from all compartments. Squeeze foam sections gently (never wring) to push water out.
- 6
Air dry upside down in a ventilated area — 24–48 hours
Hang the pack upside down with all compartments open to allow full air circulation. The interior foam padding takes significantly longer to dry than the shell — press on shoulder straps and back panels to check if they are still damp after the shell has dried. Never store the pack until all foam sections are completely dry. Direct sunlight for UV is fine on nylon and polyester but avoid prolonged UV on PU-coated sections.
Component-by-component guide
| Component | Material | Machine wash | Hand wash | Risk |
|---|---|---|---|---|
| Shell fabric | Nylon 6,6 or polyester, DWR coated | Technically possible on delicate cold — but risks DWR loss from detergent residue | Hand wash with technical cleaner, cold | DWR degradation from surfactant residue; no structural risk |
| Frame sheet | HDPE/LDPE polyethylene or aluminium | No — spin cycle deforms PE sheet; wet aluminium corrodes | Remove before washing; wipe with damp cloth | Permanent deformation (PE); corrosion (aluminium) |
| Foam padding (shoulder straps, back panel) | Open-cell polyurethane foam | No — saturates completely; very slow to dry; mould inside | Compress gently with hands to flush water through; long drying | Internal mould from incomplete drying |
| Internal PU coating (laptop sleeve, base) | Polyurethane film | No — hydrolysis accelerated; delamination | Wipe interior with damp cloth; air dry open | PU hydrolysis and delamination from agitation + water |
| Metal zippers (teeth) | Nickel-plated brass or stainless steel teeth | Not ideal — teeth can misalign under agitation | Lubricate with wax after hand wash | Tooth misalignment causing binding |
| Coil zippers (nylon) | Nylon 6 monofilament coil | Tolerates gentle cold cycle | Re-lubricate with zipper wax after washing if stiff | Wax lubricant washed out — stiffness |
Frequently asked questions
Can you put a backpack in the washing machine?
Generally not recommended. The spin cycle can deform polyethylene frame sheets permanently. Open-cell foam padding in shoulder straps and back panels saturates with water and can harbour mould during slow drying. Internal PU coatings can delaminate. Detergent residue destroys DWR water repellency. Hand wash is safer and takes only slightly longer.
How do you get the smell out of a backpack?
Musty backpack smell is usually mould or bacteria in the foam padding or main compartment from storing damp items. Wipe the interior with a solution of white vinegar (1:4 with water) — vinegar kills mould and neutralises bacterial odour compounds. Leave open with all compartments unzipped in direct sunlight for several hours. For persistent smell, a baking soda sachet left inside for 24 hours adsorbs remaining VOCs.
How do you clean the inside of a backpack?
Turn the pack upside down and shake out loose debris. Wipe with a damp cloth and a drop of mild dish soap. For sticky spots, a soft brush. Rinse by wiping with a clean damp cloth. Leave open with all zips unzipped to air dry. For PU-coated interiors (laptop sleeves, hydration compartments), only use a barely damp cloth — sustained water contact accelerates PU hydrolysis.
How do you remove mould from a backpack?
Brush off dry mould outdoors first. Wipe affected areas with white vinegar (undiluted or 1:1 with water) — acetic acid disrupts mould cell membranes. Let sit for 10–15 minutes, then wipe clean. Dry in direct sunlight. For mould inside foam padding that has penetrated the fabric, the foam may need to be replaced as mould inside open-cell foam cannot be fully cleaned from outside.