How do I make the bay window warmer in winter?beside cover with plasti

I would use installation door and window tape and cover the outside of the window inside. Also, living in Montana, I would add a wool round rug on the floor for added warmth. If this is a sitting area, s collection of wool or burlap pillows lining the inside might help block cold on bottom . Covering half the window ( either with an insulated valance on the top, or partial clip on thermal curtains or shades on the bottom half . The clip on rings can fit on any long tension rod easily .

You can purchase insulate fabric at JoAnn's. Use a half price coupon. It is bound on 4 sides so you only have to sew a hem on the top and use a tension rod in the window. It keeps the cold out in the winter and heat out in the summer. It does make it dark though, which is great for bedrooms. All you have to do is cut and sew a hem. You cannot use hemming tape as it will ruin the insulation.

also put something in front of the door bottoms. Like a rolled up blanket or use weather stripping.

https://www.apartmenttherapy.com/how-to-make-windows-warmer-for-winter-reader-intelligence-report-198230

https://macgyverisms.wonderhowto.com/how-to/trick-keeping-your-home-warm-during-winter-for-cheap-0167933/

https://homeguides.sfgate.com/warmest-way-cover-cold-windows-60994.html

https://www.popularmechanics.com/home/how-to/a9582/how-to-winterize-drafty-windows-16024743/

Can you take off the siding from the bottom of the bay window? If so, then caulk the heck out of it, spray foam all cracks & holes, install a vapor barrier like Tyvek, put in the highest R-rating insulation you can find, like R-30. Put the siding back on and re-caulk every crack and crevice.

If you can get to the top of the bay window & sides, repeat the steps above.

If the glazing is not dual paned, gas filled, look into having new Low-E glass put in and find out what SHGC & U Factor is appropriate for your climate. They will pay for themselves in a couple of years.

Then there’s old fashioned storm windows too.

Heavy fabric drapes will help as well as an area rug in front of the window.

Fix a blanket to the back of your curtains.