Guinea pigs like to hide. It's their second nature. Why not make a little house with fleece for them. So it is comfortable, machine washable and pleasant to look at. The same technique will apply for puppy or kitten beds, just in a larger scale. Also check out my other post about DIY sewing a cage liner with fleece.
I use fleece on both inside and outside. You can use cotton, canvas, linen or denim fabric on the outside so it is less bulky to sew. The bottom can be waterproof fabric (waterproof mattress protector, shower liner, or PUL fabric). Design it anyway you like for your special pet.
You need one layer of batting (usually used for making quilt, available at most craft store). This gives the little house/ bed structure and keeps its shape.
You also need a sewing machine and general sewing supplies. Use nylon thread and thicker needle (eg. 90/14) for strength.
Depending on how big you like, Mine has a long rectangle piece: 10 x 30 inches (including about 1 inch seam all around), and 2 pieces of 10 inches diameter circles. One of the circles will be the bottom piece, and the other one will be the top. The opening will be on the long piece.
Each piece will have 3 layers with the batting in the middle. The final dimension is about 9 inches wide and 9 inches tall. It will fit one Guinea pig perfectly.
I made a slide/video tutorial of the process. You can pause it anytime. Leave a comment if you have questions.
Basically I made each piece separately and sew them together. The long piece has a round hole opening. It looks tricky to sew but it is not. Here is how to do it.
1. you place fabrics with right sides facing together and place batting on top or bottom.
2. sew all around the circle.
3. cut out the circle.
4. flip one side of fabric to the other side. Now the right side of fabrics are on the outside.
5. Sew about 1-2 inches around the circle to secure 3 layers. You don't need this step but it secures all layers more.
Sew the 2 long edges, but only the middle layer and one outer layer. Then we can sew the short edge seam of rectangle. Sew the inside and outside seams separately so we can flip inside out and hide the raw edges.
Sew the 2 circles. Place 2 fabrics facing each other with middle layer on the top. Pin and sew around the edge, leaving a few inches opening. Turn inside out through the opening. Sew close the opening. Sew a line about 1.5 to 2 inches away from the edge to secure all layers.
Sew the 2 circles to the top and bottom of the tube we just made. Flip inside out and you are done.
Pee pad or liner
Sew another circle matching the inside of the pet bed's dimension. It can be a pee pad for easy cleaning. It usually has a fleece layer, middle absorbent layer (old towel), and a waterproof layer in the bottom. Sew it the same way as the 2 circles.
Hope this is helpful. Also check out the post of DIY sewing tutorial for guinea pig cage liner.