You have to replace the filter if you are no longer able to clean it properly. This usually happens after you have cleaned it 50 times.
When to replace my Philips DailyDuo vacuum's filter
1. At a shop nearby:
Most stores that sell Philips vacuum cleaners also sell filters and dust bags for these vacuum cleaners. You can find a store in your neighbourhood that sells Philips products and accessories under 'Product Support' on the left-hand side of this page.
2. At an Authorised Philips Service Centre:
You can contact the Philips Consumer Care Centre for the address of an Authorised Philips Service Centre in your neighbourhood where you can buy filters and dust bags.
If the above solution(s) did not help to solve your problem, please contact Philips Consumer Care.