Frequently Asked Questions


For the majority of adults, we recommend purchasing our Standard (G9) size.

Our Small (G8) size is recommended for teenagers and women with smaller facial features (around 70% of women prefer the G9).

The G7 mask is perfect for kids from 7-11 so now the whole family can get Castle Grade protection!

The G-Series filter has been lab tested by several third-party labs. Results from these tests have shown a level of filtration efficiency over 95% consistently, with Nelson Labs performing the NaCL aerosol challenge test which returned a >98% efficiency score for a median particle mass of <0.3 microns. (The standard for N95 Masks is 95%)

G-Series vs Fabric Masks: Most fabric or cloth masks provide very little protection against viruses which can remain active on fabric for days.  These types of masks hold moisture, which reduces efficacy over time and can in some circumstances can actually create greater risk of exposure to the wearer.

In response to the increasing use of fabric masks due to COVID-19, Duke University researchers conducted a study which demonstrated significant shortcomings and can be found here.

G-Series vs Disposable Surgical Masks: Disposable surgical masks, while providing some protection, do not provide an air seal in the way respirator masks like the G-Series do.  Respirator masks ensure the air is filtered in and out of the mask and does not escape around the sides, which has the added benefit of avoiding fogging of glasses.  Sadly, the wearing and improper disposal of surgical masks is already creating enormous waste and polluting our streets and waterways.

G-Series vs N95 Respirator Masks: N95 respirator masks provide a high level of protection comparable to the G-Series mask, however they can be uncomfortable to wear over long periods, causing skin irritation in some people.  They are also expensive if worn frequently, wasting a large amount of expensive N95 filter material.  As a re-usable mask with replaceable filters, the G-Series can be cheaper to own over as little as a week of use.

For hygiene reasons, we cannot accept returns on our masks and filters.  In the unlikely event that you experience any issues with the product, please contact us at and we will be pleased to help you.

Remove the 4-ply filter and if reusing, set it aside on a clean napkin.  Place the mask in the dishwasher in a normal cycle. You can also submerge it in boiling water for 2 seconds or use an autoclave steriliser. If you prefer to keep it clean throughout the day you can wipe it down with any disinfectant.

You can wear the mask for up to 1 week or 32 hours of direct use, before replacing the filter.

Don’t! Keep the mask and buy replacement filters on our website when you are running low or sign up for the subscription so you never run out. We cringe seeing so many masks being discarded after just one day of usage and Mother Nature needs your help.

The G-Series Mask is registered as a Class I Medical Device with the TGA in the Australian Therapeutic Goods Registry (ARTG) registration number 341649