Floor insulation - what to look for
If there is any bulk insulation in your crawl space then it will usually be installed between the joists under your floorboards.
Some older homes have a very low space under the floorboards which makes it impossible to see how much insulation there is. If this is the case you should assume there is no underfloor insulation.
Look for a label like the one in the photo below. This will tell you the R-value (how warm the insulation is) and how thick it was when it was installed.