I've frequently seen (and answered) gear storage questions on the Reddit Ultralight forum, and it seems like an article may be helpful. Through the decades, I've also seen just about every gear storage disaster possible; there's a sad story behind every one of the suggestions below. It's better to learn from someone else's misfortune than to experience it ourselves.
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Optimal gear storage for longevity: clean, dry, loose, cool, dark.
Things to avoid:
mildew – store gear dry and prevent moisture wicking.
odor retention – store gear in breathable containers, or hanging up.
soiling or staining damage – store gear clean.
stress on seams and fabrics – store loosely stuffed, use fat hangers.
UV light damage – store gear in the dark.
heat damage – store gear cool.
compression damage – store insulation loose and soft.
insect / rodent damage – store gear clean, protected, and inspected.
Mildew: keep your gear dry and prevent moisture wicking.
Tents and shelters are the gear most commonly damaged by mildew, although any fabric or insulation material can mildew, as can maps and notebooks. The usual problem comes from packing up a damp or wet tent in the morning, and then putting it straight into long term storage upon return home. The way to avoid this is to make sure that things are stored as dry as possible.
For these reasons, exercising diligent gear care is of paramount importance. Give your gear attention during a long hike. If a tent or shelter was packed up on a wet morning, try to take a mid-day break and dry it out. At the end of a hike, all gear, especially shelters, should be hung up to dry completely, fully spread out on a clothesline, and not stored until you are sure it is bone dry and clean enough to not damage fabrics.
Once your gear is dry, keeping it dry during storage is just as important. In dry climates, dry storage is quite easy. In humid climates, it’s much more problematic. In a controlled and air-conditioned indoor environment you will probably be OK, but in some places you may wish to consider getting a dehumidifier for your gear closet.
Do not store gear sitting on a concrete floor. For one thing, the floor will always be cooler than the surrounding air, and you will have a constant condensation layer on the bottom of your gear. Also, concrete is porous, and it will wick moisture from the ground up into cardboard boxes, bags, wood trunks or footlockers. Any of these will create mildew. Place boards on concrete floors to make an air space underneath any storage container.
Odor retention: store gear in breathable bags and containers, or hanging up in a ventilated place.
Over long time periods, odors can accumulate and intensify. Sometimes these odors are part of the fabric manufacturing process, and they can become objectionable if concentrated. Do not store gear in air-tight bags, bins or containers.
Soiling or staining damage: Before long term storage, inspect your gear for excessive dirt or other soiling, and clean as needed.
If you have ever washed and stored a “clean” white cotton shirt for a long time period, you may have been surprised to find that it was yellowed, filthy and stained when you got it back out a few months later, especially around the neck and collar, and in the armpits.
The reason for this is usually oil-based. Skin oils, like almost any oils, will oxidize and polymerize over long periods, slowly transforming from an oil into a grease, and then finally hardening into a solid varnish. This will not only stain fabrics, it can also rot them.
For this reason, storing dirty gear is a risk, especially if it is dirt that results from direct contact with the human body. It’s relatively easy to clean a recently soiled piece of gear, but it’s an arduous task to clean gear when the body oils and salts have polymerized into solids, rendering fabrics stiff, greasy to the touch, weakened, and discolored.
Any stain from a biological source will be problematic when it’s allowed to “set” and solidify over time. This includes stains from humans, vegetation, tree sap, algae, organic-rich mud, animals, food, and beverages.
Because of those same biological concerns, cooking gear should always be completely clean and dry when stored.
Inorganic mineral dust will also damage gear, as it will act as an abrasive embedded into the fabric fibers, and it can completely jam and destroy zippers and fasteners.
Stress on seams and fabrics: store loosely stuffed, or roll gently, use fat hangers, do not compress.
Ultralight fabrics are fragile. Stuffing tightly, rolling tightly, and dense compressing all puts stress on these fabrics, and this is compounded when the stress is maintained over long time periods. Seams can easily rip and pull apart, and fabrics can be distorted, stretched, de-laminated, and weakened.
Store sleeping bags and quilts hanging up full length, or very loosely stuffed into a large breathable bag. This storage bag should be large enough that there is some extra room left over after it is closed, with no compression. For some items, old pillow cases can work very well, especially king size. A drawstring is relatively easy to add.
Tents and shelters should also be stored very loosely stuffed into a large breathable bag, or in a breathable box or container large enough to hold the materiel with very little to no compression. Loosely and randomly stuffed is better than rolled or folded, as it prevents repeatedly creasing the fabric in the exact same spots.
Sleeping pads should be stored stress-free as well. Closed cell foam (ccf) pads can be stored flat, or rolled very loosely with no compression. Long term compression with cords or straps will cause permanent deep grooves and creases. Inflatable pads should be stored very lightly inflated, using dry room air, rather than your moisture-laden breath. Inflate them enough so they hold a soft shape, but not under pressure. Some people hang their pad vertically, which is fine as long as you don’t damage the fabric around an air chamber with hooks or clips. You can also store inflatable pads flat on the floor underneath a bed, or standing on edge lengthwise.
Clothing should be hung up using “fat” hangers, not plain wire, to avoid stretch, creasing, and fabric de-lamination damage to the shoulders. Hanging provides the least stress on fabrics and seams, and the maximum ventilation to prevent odor accumulations. Thicker / heavier insulated coats benefit from bag storage instead of hanging.
Hang your pack up on a fat peg or hook. Don’t use a wire hanger, which can cause long-term crease damage to fabrics or shoulder strap padding.
UV light damage: keep your gear in the dark.
Ultraviolet light will rapidly fade and slowly rot any fabric over time, and it can damage seemingly impervious materials like plastics and metals.
Heat damage: keep your gear cool.
You wouldn’t think this was a common issue, but in hot environments, vehicles, attics, garages and storage units can easily get hot enough to damage some gear. Plastics melt at relatively low temperatures, and many kinds of fabrics and insulation are basically plastics, and hence easily melted, weakened, and made brittle. Other materials can be damaged at lower temperatures than you might expect. For this reason, look for a cool place to store your gear, and also avoid storage next to a water heater, home heating furnace, fireplace, or above kitchen stoves or appliances.
Compression damage: store gear loose and soft.
Compression damage can not only affect fabrics, it can especially compromise insulation. Long-term compression is generally not a good thing, and while people argue about this all the time, there’s absolutely no point in risking it for off-season storage. Besides, compressed storage means your gear can’t breathe, and you also risk fabric stress damage.
Insect / rodent damage: clean, protected, and inspected.
Finding a sleeping bag which has been turned into a condominium for mice is very irritating. And finding merino wool items perforated and excavated by wool moth larvae is equally annoying. It helps to make sure your wool / alpaca / etc gear is clean when stored, because moth larvae need the oils and salts to thrive. Make sure that gear vulnerable to these pests is protected by breathable covers. Periodically inspect your stored gear to stop infestation damage before it becomes more extensive.
If you have a wool moth problem, here’s how to to make sure your merino gear is safe: after it is clean and dry, seal it into a ziplock bag and leave it in the freezer for a week or so. This will kill all moth eggs and larvae.
Water Filter Storage:
Soak the filter in warm white vinegar for thirty minutes to one hour to dissolve mineral deposits and buildup.
Back-flush forcefully and repeatedly with distilled hot water (hot to your hand, but not burning.)
Repeat 1. & 2. as needed until flow rate is restored.
Test and flush with distilled water until no vinegar flavor or odor remains.
Soak in an Aquamira solution to completely disinfect.
Shake dry until no water comes out either end.
Store in a breathable bag or container.
These steps should refresh your filter back to “like new” condition and flow rate for the next season, and insure safe storage.
Soak your filter in distilled water and test before the first trip of the next season.
Oddball extra tips:
Do not store your compass near a strong magnet. Several backpack manufacturers use these for hydration tube holders, and some pack makers use magnets for top closures.
Remove alkaline batteries from flashlights and devices before long-term storage; they can leak and completely destroy gear.
Check your pack, clothing pockets, hipbelt and shoulder strap pockets, and fanny pack for leftover snacks before storing.
Turn tents inside out and give them a few shakes to make sure all dirt, sand, and bits of vegetation are gone before storing.
The number one cause of broken gear buckles is catching them in closed vehicle doors and trunk lids. The number two cause is stepping on them.
Taken together, all of these protocols add some extra time and energy to your gear storage, but they can help you keep your gear in great condition for decades.