The pattern I used came from Craft Passion on YouTube. I loved this tutorial, because it was concise and there was no talking! Too much chitter chatter makes for a way too long video, and this one is just what the crafter ordered. This YouTube video also contains the link to the free pattern, which comes as an SVG file as well in case you want to cut a template out on your cutting machine.
I used a really fun idea on these. I do a lot of paper crafting, and for the past eight years I have been printing my own patterned card stock. I also do lots of HTV and transfers with images applied to fabric (t-shirts, onesies, etc.) with my heat press. I decided to use white lining fabric and heat press patterned paper onto it, then use it for the masks. So, the top one is a Carta Bella patterned cardstock (Cowboy Country) which was made for my husband. It reminded him of his childhood in the 50s. The second one was designed by me for my daughter using linguistics letters (if that's what they're called?). The third for my niece, a flight attendant, and the fourth a fern pattern for my brother. This was such a fun way to personalize the masks. I believe the rest I made were just old scraps from my quilting days many years ago.
This is a really well thought out pattern, with an opening in the back to insert a filter. It's a free pattern that comes in many sizes. The link for the pattern is in the tutorial, as mentioned above. The following link gives good information about how to make the most efficient face mask and what materials you might want to use when making a mask. The Fabric Patch.
Best wishes! Stay safe!