The humidity reality
Kolkata's monsoon is not just rain — it is sustained, intense humidity for four consecutive months. During June through September, relative humidity in Kolkata consistently exceeds 85% and regularly approaches 95–100% during and immediately after rainfall. This is not simply uncomfortable for people. It is actively hostile to stored organic materials — fabric, leather, paper, and wood.
At 85%+ relative humidity, organic fibres absorb moisture from the air. Silk — a protein fibre — absorbs approximately 11% of its weight in water at normal humidity. At 95% humidity, this absorption is significantly higher. A stored silk saree in Kolkata's peak monsoon is not dry. It contains significant moisture that it absorbed from the air around it.
Mumbai's monsoon is intense but shorter and more variable. Delhi's monsoon is significantly less humid than Kolkata's. Kolkata's combination of high temperature (35°C+) and extreme humidity is particularly demanding on organic materials. Garment care advice written for other Indian cities is often not adequate for Kolkata's specific conditions.
Silk and stored garments
Stored silk during a Kolkata monsoon faces three specific risks: mould, salt bloom, and dye migration. Each is caused by the humidity, and each causes different damage.
Mould grows on silk when humidity provides moisture and any organic soil (body oils, food residue) provides nutrition. Mould on silk appears as grey or black spots or patches and is difficult to remove once established. Prevention requires clean fabric, breathable storage, and humidity management.
Salt bloom — the migration of tanning salts to the surface — is more common in leather but can occur in some textile dyes. It appears as a white haze or powder on the fabric surface.
Dye migration occurs when moisture causes dye to move from dark-coloured areas to light-coloured areas in stored garments. It is most common when differently-coloured garments are stored in close contact in a humid environment.
"We see the results of Kolkata's monsoon every October when the trunks are opened. The garments that come in with problems are almost always the ones that were stored damp, in plastic, or without cleaning."
Drying cotton in the monsoon
The everyday challenge of the Kolkata monsoon is not the silk in the trunk — it is the cotton shirts that need to be washed and dried every day. Drying cotton in 90%+ humidity without direct sun is genuinely difficult, and the characteristic smell of monsoon-dried clothing is familiar to every Kolkata resident.
The practical solutions are not glamorous but they work. A ceiling fan directly over the drying rack makes a significant difference — moving air over the fabric surface removes the humid boundary layer and accelerates drying. An electric clothes dryer eliminates the problem entirely for everyday cotton. Ironing slightly damp cotton with a hot iron kills surface bacteria that cause the musty smell.
Woolens during monsoon
If woolens were properly prepared and stored before the monsoon began, they should be largely undisturbed during the monsoon. The most important action is to verify this in July — after the first heavy monsoon humidity surge — without fully unpacking.
Open the storage container briefly. Smell for mustiness or mildew — this is the first sign of biological activity. Look without handling for any visible mould or discolouration. If everything appears normal, close and leave. If there are any concerning signs, remove the affected garments immediately.
Remove the affected garment from the storage container immediately. Do not fold or pack it — lay it flat in a ventilated space while you arrange for professional dry cleaning. Check all garments in the same container for early signs of spread. Take the affected piece for professional cleaning within 48 hours — do not wait for October.
Post-monsoon care in October
October is the most important month in the garment care calendar in Kolkata. The monsoon has ended. The temperature is dropping. Woolens and heavy fabrics are needed again. And everything that was stored during the monsoon needs assessment before use.
The post-monsoon protocol: open every storage container and assess the contents. Air everything in dry October air — hang items outside in the early morning sun if possible. Any garment with mould, mildew, musty smell, or visible deterioration goes for immediate professional cleaning. Clean garments are re-stored correctly for the short Kolkata winter.
October is our highest-volume month of the year. Post-monsoon assessment and cleaning of stored garments, combined with pre-Puja preparation of occasion wear, creates a significant peak. We recommend bringing in post-monsoon garments in the first two weeks of October to ensure availability before Puja.
The Swiss Laundry operates through the monsoon — Monday to Saturday, year-round. Pre-monsoon cleaning in May, mid-monsoon emergency treatment when mould is found, post-monsoon recovery in October. 13 monsoons in Kolkata have given us specific knowledge of what the city's climate does to stored garments.