I was looking for an alterative to fish paper for wrapping my LiFePo4 cells before reinserting them into my battery case. Why wrap cells? To keep them physically separate and prevent any errant electrical connections.

The usual wrap is something called Fish Paper, which doesn’t have much to do with fish (as far as I can tell) and really isn’t paper. Fish paper is relatively expensive in the quantities I needed and not readily available to a non-commercial user like me.

It turns out a good substitute in this case can be found at the post office for free– Tyvek mailers. Tyvek is spun polyethene that has the characteristics of fish paper. It’s also tear resistant, breathable, and waterproof. The envelopes have the added advantage of a self-adhesive strip to speed the wrapping process. You can find them here:  https://store.usps.com/store/product/shipping-supplies/priority-mail-tyvek-envelope-p_ep_14

Here’s a wrapped cell:

Thank you, US Postal Service!