A filter is a question you let the customer ask. Most stores offer twenty questions nobody asks and hide the three that decide the sale. The fix is not more filters. It is the right ones, in the right order, always visible.
Start from the questions people ask you
Read the last fifty support emails and chat transcripts. The questions that repeat are your filters: does it come in my size, is it vegan, will it fit a king bed, is it in stock. If a filter does not answer a question someone has actually asked, it is decoration.
A filter is a question you let the customer ask. Offer the ones they ask.
Five, not twenty
Size, colour, price, and two that belong to your catalogue. Everything else goes into search or onto the product page. Twenty checkboxes is a form, and nobody came here to fill in a form.
Use their words
"Vegan", not "plant-based formulation". "Fits a Toyota", not "compatibility group C". The label is the customer's vocabulary, which you will find in the reviews and the emails, not in the supplier's spreadsheet.
Keep them where the thumb is
On a phone, filters belong in a bar at the top of the grid that stays put as it scrolls, with the active ones shown as chips. Hiding filters behind an icon and a drawer is hiding the reason the customer stayed.
Show the count before they commit
"Blue (14)". A number beside each option tells people what they will get before they tap, and prevents the empty page that sends them back to the search engine. If an option would return nothing, do not offer it.
Make undoing obvious
Every active filter is a chip with a cross on it, and one link clears them all. The quickest way to lose a shopper is to trap them in a filtered view they cannot see their way out of.
Fewer filters, in their words, always visible. That is the whole job.
