"As soon as we went to Level 2, it got crazy," Nicola said.
Doug said more people had been asking about masks than bikes.
"The masks are the thing at the moment. If we were to move into a higher level, the masks at some stage may become a mandatory thing," he said.
"This is a preventative measure to stop any spread and that's what the mask is designed for."
Nicola wanted the masks to be accessible for all, and is charging $12 for each one.
"I have friends in Australia saying that I should be charging more. But if you're a family and you want to have a couple for each person, that quickly adds up," she said.
Each mask takes 15 to 20 minutes to make.
"It has shape to it. Some just wrap around, these fit over the nose and face a bit better."
Nicola has been working "basically around the clock" trying to catch up on orders and to assemble a decent stock heading into the weekend.
"The other night she was up until 1am. I rolled over and saw her sewing away," Doug said.
The masks can be made with various designs and patterns, which the Rennies hope will encourage people to be more open to wearing them.
"The bonus is not everyone will be walking around with a white paper mask or a black mask, there are a lot of designs.
"If you can make kids' ones and make them keen on wearing something that looks cool, that's a good thing."