MDF.

1959 exterior siding from TX. Other than that, none.

Shiplap wasn never meant to be interior wall treatment and why do you think you need it . Maybe post a pic of what you think shiplap is . That whole look has become very dated too

There are options to get this accomplished but they might be a bit pricey.

Here is a shiplap bathroom blog.

https://nestingwithgrace.com/azek-the-best-shiplap-for-bathrooms/

https://www.lowes.com/search?searchTerm=azek

What you'll need is a board that will not absorb water or humidity AZEK makes PVC exterior white trim that comes in a variety of thicknesses and heights that can be used in the bathroom and even in the shower.

https://www.savvyinteriors.com/designblog/shiplapshower

Your other option is to use porcelain tile, designed to look like flooring on the walls of the bathroom and or shower.

Trends come and go, but if you really like the shiplap look, go for it. Just make sure you pick the right material and finish so it actually holds up in a bathroom.

If you like shiplap, go for it but DO NOT use MDF. MDF absorbs moisture and blows up like a sponge. Take Beverly's recommendation for PVC.

Would suggest a totally synthetic material like Azek. Should absorb moisture as it is a cellular pvc. Would discorage you from using a synthetic and wood fiber composite. Those are supposed to hold up well under wet conditions but just don't think I would take the chance on it.

Here we go not one remark from the OP I love it when we take time to answer and they have no time to reply. 8 days really ??

Well in fairness, everyone told her it couldn't be done. Did you expect her to be joyful?

This is true.

Thank you for all your input

Patricia Colwell Consulting, You're a bit grumpy. You have no idea what has been going on in my life. I definitely wouldn't use your services