How to store 3D printer filament in a Canadian home: humidity, basements and winter

Why the season matters as much as the room

Most filament storage advice is written as if humidity stays the same all year. In much of Canada it doesn't. A summer basement can sit in the damp range for weeks, while the same house in January can be drier than a desert indoors.

A classic National Research Council Canada building digest explains why. Cold winter air holds very little water. When it's warmed indoors, its relative humidity drops sharply. The digest's example compares Ottawa and Vancouver in January. Both have similar outdoor humidity, but once that air is heated to room temperature, Ottawa's falls far lower because the outdoor air started out so much colder.

Summer works the other way. Health Canada's guidance on moisture and mould recommends keeping indoor humidity between 30% and 50%. It says to run a dehumidifier when it goes above 50%, and to use one in damp basements year-round if needed. Those targets are about protecting your house, but they are also a useful benchmark for filament.

What humidity filament actually wants

Even a well-run home is too humid for long-term filament storage. Bambu Lab's drying guide says typical indoor air is usually 45% to 65% RH and higher in wet weather. Most filaments only stay dry for a limited time below 20% RH. Once dried, filament at 20% RH generally stays dry for 2 to 7 days. At around 55% RH, a freshly dried spool can absorb enough moisture to affect print quality within 2 to 12 hours, depending on the material.

CNC Kitchen's Stefan Hermann gives a similar target. In his write-up on a desiccant storage cabinet, he advises keeping filament below about 20% RH, and his cabinet held roughly 15 to 16%.

Not every material is equally sensitive. Owners on the Prusa forum describe PLA, PETG, ABS and ASA as fine at around 30% RH for short periods, perhaps a week. They say TPU, nylon and polycarbonate need much more care. Prusa's knowledge base agrees that TPU, nylon and PVA need drying far more often than PLA. Bambu calls TPU highly hygroscopic and tells owners to seal it with desiccant as soon as a print finishes.

Basements: convenient, but check before you commit

Basements are where many Canadian printers end up, and the results vary. One long-time PETG user on the Bambu Lab community forum stores open spools in a basement averaging about 16 °C and 78% RH. He says drying makes only a small difference for him. Other owners in the same thread strongly disagreed, and some brands in the discussion were described as far more moisture-sensitive than others. Treat that thread as proof that results vary, not as permission to skip storage.

Health Canada's advice for damp basements also applies to filament. Check for damp spots, keep cardboard boxes off the floor, and store items in lidded plastic bins. If your hygrometer regularly reads above 50%, run a dehumidifier with the windows closed, and empty or drain it regularly.

Cold is a separate issue for printers that dry filament. Bambu's AMS 2 Pro spec sheet says its maximum drying temperature of 65 °C is only reached when the room is above 25 °C. In a cooler room, the actual drying temperature may not reach that maximum. A basement in the mid-teens is well below 25 °C, so expect slower or less complete drying there than the settings suggest.

Winter: dry air helps, but don't count on it

Dry winter air works in your favour, but it isn't a substitute for sealed storage. Natural Resources Canada's Keeping the Heat In guide shows that the indoor humidity a home can hold before windows fog depends on the glazing. At −20 °C outside, its table gives a maximum of 34% RH for standard double glazing and 50% for double-glazed low-E windows. The NRC digest also notes that people and everyday activities add moisture indoors. A humidifier, cooking, showers or drying laundry can push a single room well above the house average.

The only way to know what your filament is experiencing is to measure it. Health Canada notes that hygrometers are inexpensive and sold at most hardware stores. Put one where the spools live, and another inside each storage bin.

A practical storage setup

Use a lidded bin with a good gasket. Owners on the Bambu forum and the Prusa forum mostly use sealed plastic tubs, vacuum bags or dedicated dry boxes. Prusa's knowledge base recommends closed containers with desiccant and says vacuum bags with desiccant are a popular option.

Add plenty of desiccant. CNC Kitchen found that a sealed box with a generous amount of silica gel pulled significant moisture out of undried PLA and PETG over a week. He sees good storage as part of drying, not just the step after it.

Put a hygrometer in each bin. Colour-changing beads only tell you roughly when the desiccant is used up. A digital reading tells you when to act.

Prioritise by material. If space is tight, Prusa suggests giving the best storage to the most moisture-hungry filaments. For most people that means TPU and PETG first and PLA last.

Keep spools in their original resealable bags if they came with one. Polymaker, for example, describes its PETG packaging as a resealable vacuum barrier bag for this purpose.

Recharging desiccant

Silica gel needs regular regeneration, more often in humid summers. Bambu's guide says not to heat silica gel above 100 °C. It suggests 80 to 90 °C in an oven, spread no more than 2 cm deep, for 1 to 3 hours depending on how saturated it is. Use a dedicated tray rather than cookware. Bambu also says enclosed models such as the P1S can do the job on the heated bed at 80 °C for 3 to 4 hours.

CNC Kitchen regenerates at 110 °C for 2 hours, so published methods differ. Follow the instructions for the specific desiccant you bought. Bambu adds that silica gel can typically be regenerated 5 to 15 times and should be replaced once the beads crack or change colour slowly.

Seasonal checklist

Spring and summer: run the basement dehumidifier when readings go above 50%, recharge desiccant more often, and dry PETG before long prints.

Fall: check bin seals and replace tired desiccant before the heating season.

Winter: open bins less often in rooms with a humidifier. Expect drying in a cold basement to be slower than the dryer's display suggests.

Year-round: dry filament when it shows symptoms, then return it straight to sealed storage. Bambu's guide warns that freshly dried filament left in a typical room can absorb enough moisture to affect prints within hours.

From a tech standpoint

In Canada, the season matters more than the room. A sealed bin with fresh desiccant and a hygrometer inside handles both humid summers and dry winters. Aim for the under-20% RH figure Bambu and CNC Kitchen point to, and keep your house in Health Canada's 30 to 50% range. If the printer lives in a cool basement, plan on longer drying cycles.