Glass and porcelain
Red tea is fully oxidised, so the material has less power over it than in any green category.
Water at 95 °C or above is standard, and a vessel holding that heat is doing useful work.
Glass and glazed porcelain are still the neutral choices, and both show the liquor honestly.
Colour matters more here than anywhere else, because it is how a red tea is judged.
A white interior shows the true colour, and a dark glaze hides it completely.
Porcelain is the traditional match, and a 250 ml pot with a lid is the usual form.
It holds heat better than thin glass, which a fully oxidised leaf appreciates.
Heat retention is an advantage here rather than a problem, and that reverses the green tea logic.
A thick walled porcelain pot keeps the water near boiling through a long steep.
Glass loses heat faster and gives a slightly thinner liquor, which some drinkers prefer.
That is a real difference and worth testing, since neither one is wrong.
Both are non porous, so either can be rinsed clean and used for something else tomorrow.
Clay
Clay is a genuine option for red tea, and it is the one category where that is true from the start.
A fully oxidised leaf tolerates the extra heat, and the thicker wall keeps a long steep hot.
Zisha（紫砂）pots are the usual form, and the material has been paired with red tea for centuries.
The pores take up oils from the liquor and build a layer over months of use.
Drinkers describe the effect as rounder, and it shows up as a slightly thicker mouthfeel.
Absorption is the other side of it, and it is a commitment rather than a benefit.
A pot seasoned on red tea will make red tea, and it will not make anything else honestly.
Brew a delicate white tea in it and the background note arrives whether you wanted it or not.
Seasoning takes about a year of regular use, and it cannot be rushed or transferred.
A pot sold as already seasoned was seasoned on something, and nobody can tell you what.
Buying one means deciding which tea you will still be drinking in two years.
That is the real cost of clay, and it is not the price on the label.
Matching to the tea
Match by brewing style first, since red tea is brewed long and short more than any other category.
A 3 minute steep in a 250 ml pot wants a vessel that holds its heat.
A 30 second infusion in a 100 ml gaiwan wants one that pours fast instead.
Those are different vessels, and the material follows from which style you use.
Porcelain suits both, and clay suits the long style better than the short one.
Fix the dose at 5 grams in 100 ml and weigh it, and the material question shrinks further.
Match by grade second, since a whole leaf grade and a broken grade behave differently.
Broken leaf gives up everything quickly and needs a vessel you can empty the moment you choose.
A whole leaf grade brews more slowly and rewards a pot that keeps the temperature up.
Match by origin third, and mostly to decide whether you want the aroma or the body.
Qimen is built on aroma, and a lidded porcelain vessel keeps that in the cup.
Dianhong is built on body, and a thick walled pot shows it at its best.
Buying advice
Buy porcelain in the size you drink from, with a white interior and a lid that fits.
A 250 ml pot and a 100 ml gaiwan between them cover every red tea you will meet.
Check the spout pours cleanly, since a dribbling pot costs you time on every infusion.
Check the glaze is intact, and reject anything with craze lines or pinholes.
Ignore stories about the clay, the kiln and the maker, since none of them reach the cup.
If you do want clay, buy it last and dedicate it to one tea for good.
Avoid anything sold as zisha（紫砂）for under twenty dollars, which is slip cast and coloured.
Warm an empty pot and smell it, and put it back if there is any chemical note.
Real hand built clay costs more than that, and the cheap version is coloured casting.
Spend the difference on a whole leaf grade, which changes the cup far more than any material does.
A whole leaf Dianhong in a plain pot beats a broken grade in anything you care to name.
Cheap neutral ware and good leaf, and the category is covered either way.