Train 42 from Hat Yai Junction to Hua Lamphong Station in Bangkok is an air-condition Diesel Railcar (also known as a Sprinter Train). These are the fastest of all rail services on this route and comprise of just a few carriages.
There are only 2nd Class seats in air-conditioned coaches on this service.
Included in the ticket price are airline style meals and soft drinks - they are not that great, so you may want to bring some snacks of your own, as unlike most Thai trains, food hawkers rarely get a chance to come on board to sell their goods.
These DRC Sprinter trains are quite comfortable, with reclining cushioned seats arranges in pairs along the carriage.
The air-conditioning can be quite cold, some bring something warm to wear for this long trip.
Tickets for this route are available to buy up to 90 days in advance.
We would highly recommend you book your seats as far in advance as you can (especially if you are travelling during the main tourist season of November to April).
Hat Yai Railway Station has it's own advance booking office (located on the left as you enter the front of the station), so if you want to see what seats are available on any trains to Bangkok from Hat Yai, it is best to go there as soon as you know when you want to leave the city.
Many trains to Bangkok can get fully booked quite far in advance, so if you already know your travel dates, it is best to book your tickets before you arrive in Hat Yai.