After my great vinyl purge of 2016, I was left with only a few hundred records, one record player, and no slipmat. Rather than not use the record player, and not make a pressure-purchase on Amazon, I figured I could DIY a slipmat with arts and crafts supplies. Seeing as many commercial slipmats are nothing but a felt circle, it couldn't be that tough...

Step 1: Gather the Materials

Gather your materials onto a clean, well-lit surface.

You will need

Thin cardboard, at least 12" x 12". I used a generic record sleeve. This is the same weight as a cereal box. You could probably go a little heavier.
12" Record You will use it as a template, so find one you don't mind scuffing up.
Scissors, Knife, Pencil. The usual random arts and crafts tools are fine.
Felt, at least 12" x 12". The photo here shows fleece. I compared the two fabrics and found that while the fleece was softer, it pilled and would be prone to make a mess. Maybe some finer fleece would be ok. You'll have to find what's in your scrap pile.
Hot glue gun and glue.

Step 2: Trace the Template

Using the record as a template, trace its shape onto the cardboard.
Be sure to trace the center hole as well.

Step 3: Cut the Template

Cut the traced line to create a round 12" piece of cardboard.
Cut out the center hole too.

Step 4: Cut the Felt

Place the cardboard backing over the felt
Cut the felt around the cardboard

TIP: As a lesson learned, make sure that the felt is larger than the cardboard, unlike I've done here. You will trim it later, not in this step.

Step 5: Glue the Felt to the Cardboard

Heat up your glue gun. Remember that hot glue solidifies quickly, so work quickly.

Apply a dab of glue to the cardboard and correctly place the felt to anchor in place.
Once held in place, run lines of glue across the cardboard, from one side to another, quickly followed by laying down the felt.
When done, trace the outermost edge of the circle with glue.