By the end of a hot summer, well-worn cork sandals tell the truth about your July. The footbed has gone dark and shiny in the shape of your foot, the straps have a dusty bloom on them, the cork edges look pale and thirsty, and there is a faint smell you are choosing not to investigate. This is completely normal and almost entirely reversible. What is not reversible is the damage done by the two things most people instinctively reach for: a washing machine and a lot of water. Learn the material map, and a pair you love will comfortably outlast the trend cycle.
Know what you are actually cleaning
A classic cork-soled sandal is three different materials pretending to be one shoe, and each wants something different. The straps are usually smooth leather, nubuck or suede. The footbed is generally suede-lined over a cork and latex core. The cork rim around the edge is sealed with a thin protective coating, and that seal is the weak point — once it wears through, water gets into the cork, and cork that gets soaked and dries repeatedly crumbles.
Moulded single-material sandals, the rubbery ones designed for pools and rain, are the exception. They can be rinsed under the tap, scrubbed with a soft brush and a drop of washing-up liquid, and left to dry. Everything below applies to the cork-and-leather versions.
The footbed: dry brush first, then barely damp
Start dry. Take a soft brush — a suede brush, a clean nail brush, even an old toothbrush — and work over the whole footbed to lift dust and loose grime. A surprising amount comes away at this stage, and dry dirt turns to mud the moment you add water, so never skip it.
Then tackle the darkened areas. Sprinkle a little bicarbonate of soda over the footbed, leave it for an hour or two to absorb oils, and brush it out. For remaining marks, mix a drop of mild soap into a small bowl of water, dip the brush and shake off the excess so it is damp rather than wet, and work in small circles from the heel forward. Wipe the lather away with a barely damp cloth as you go. Keep every bit of moisture on the suede surface and off the exposed cork edge. Once dry, brush the footbed again to restore the nap, which is what makes it look freshly matte rather than glazed.
Straps, cork edges and the drying rules
Smooth leather straps take a wipe with a soft cloth and a very small amount of mild soap, followed by a leather conditioner or cream once dry. Suede and nubuck straps are a dry-first job: brush the nap, use a suede eraser on scuffs, and only spot-treat with a damp cloth if you must. Buckles can be wiped with a dry cloth; leave metal polish out of it, as it stains leather.
For the cork rim, brush off dust and check for hairline cracks or a chalky, dull look. Both mean the seal has worn and it is time for a cork sealant, sold for exactly this purpose — a thin coat with a cloth or small brush, allowed to dry fully, will keep water out for another season.
Then dry properly, and this is where sandals are lost. Leave them somewhere airy at room temperature, out of direct sun, and nowhere near a radiator, hairdryer or hot car dashboard. Heat shrinks leather and dries the latex layer under the cork until it cracks. Give them a full day, ideally two, and stuff a little paper under the straps to keep their shape. Never soak them, never put them in the machine, never in the dishwasher.
Can you put Birkenstocks in the washing machine?
No — a cork-soled leather sandal should never go in the machine, and it is the fastest way to ruin a pair. The drum's water and heat break down the adhesive and the latex under the cork, and the leather dries out hard and misshapen. Only fully moulded rubber-style sandals can be safely rinsed with water, and even those are better done by hand under the tap.
How do I stop the footbed smelling?
Air them properly between wears rather than stacking them in a dark hallway, and rotate between two pairs in very hot weather so each has a day to dry out completely. Bicarbonate of soda left on the footbed overnight and brushed off in the morning absorbs a great deal, and a light sprinkle inside is worth doing every few weeks in summer.
