Thangkas without a brocade require some kind of frames. Some guidelines below.
Generally made of wood, often painted with gold, custom hard frames give the best protection for a thangka and are many times the only possibility with higher quality artworks.
There are some important things that you don't necessarily get from an averge framing shop without asking: All cardboard should be acid-free. It would be better if the paints do not touch the glass. This can be done with a colored cardboard frame between the glass and the painting (the red inner frame in the photo). All the thangkas have a 1 inch border, usually red, which will be hidden behind the cardboard frame. Also it would be better if the framer didn't use glue to fix the painting.
For the people, who can afford the absolute best, there is special non-reflecting glass, which is even difficult to see. We sometimes tried matte glass to avoid reflecting light, but didn't like the result much. It is very important to protect the painting from direct sunlight. It may be possible to find special UV-glass to protects the paints from ultraviolet rays.
Ready-made frames are an affordable way to quickly frame a thangka. If the size is good and the background carboard is of right color, they can look quite good. One problem is that the paint touches the glass and may stick after some years. Also, the edges of the canvas are not always cleanly cut. Both of these problems are solved, if you cut a colored cardboard frame, and place it between the the painting and the glass, as explained above with the custom frames.